series and parallel resistors

Hi. Actually, this is embarassing, but my question is simply an algebra question. I know the equation and I know the answer, but I can't remember how to GET the answer. Can someone please walk me through this very simple algebra issue? Equivalent resistance in a circuit = 26 ohms R1 and R2 are parallel resistors; R1 = 55 ohms R1 and R2 are in series with R3, which = 12 ohms. Find R2. The equation, as given by my professor, is: 26 = 12 + [1 / (1/55) + (1/R2)] (Answer = 19 ohms) I just can remember how to solve for that R. Thank you!

uniform electric field

"A uniform electric field produces an acceleration (10 m/s^2, 10 m/s^2,0) at (1 m, 1m, 1m) for a -5 micro Coloumb charge of mass 10 g. Write the electric field at all points in space. (Hint: it would be a good idea to know what uniform means here)." Please help me solve the problem stated above. So, uniform means constant acceleration? I'm not sure where acceleration fits into the calculations. Thank you.

draw the electric field

"For some configuration of charge, the electric force on a positive charge is F(x) = gamma |x| x hat, where gamma is a constant. Draw the electric field using arrows on a square grid with 16 points placed symmetrically about the y-axis." Please help me solve and draw the solution. By the way, is this just a point charge?

charge density

"A reasonable upper limit on the amount of charge that can be safely applied to a person is 1 micro Coloumb. What charge density must be applied to the floor to float a person with mass 50 kg and charge 1 micro Coloumb? Model the floor as an infinite plane with uniform surface charge density." Please help me solve the problem stated above. I guess I would just use the electric field formula for uniform surface charge density? I don't know.

frequency, conceptual question

Hi. Can someone please check my answer to this conceptual Q? "Although an incandescent light bulb appears to shine with constant intensity, this is an artifact of the eye's persistence of vision. In fact, the intensity of a bulb's light rises and falls with time due to the alternating current used in household circuits. If you could perceive these oscillations, would you see the light attain maximum brightness 60 or 120 times per second? Explain." Since the frequency of ac circuits in the U.S. is 60Hz -- meaning there are 60 cycles in 1 second -- and one cycle should include one Imax peak and one Imin peak, the light should attain maximun brightness 60 times per second. Thank you.