Equivalent resistance of these two circuits?

Equivalent value of resistors in parallel:

1/Rt = 1/R1 + 1/R2 + 1/R3......

So 2 ohms in parallel with 6.1 ohms in parallel with 11.6 ohms =

Rt = 1/[1/2 + 1/6.1 + 1/11.6]= 1.333 ohms

Resistors in series simply add.

1.333 ohms + 6 ohms = 7.333 ohms

So the total equivalent resistance of the first diagram is 7.333 ohms.

In the second diagram, you start by finding the equivalent of the two parallel resistors (10 and 7.2). Then add the series (4.09). Now you have an equivalent that you can combine with the parallel 3.77, then add the series 2.06 ohm.

So now you have a total equivalent resistance. Let's say that came out to 4.65 ohms.

One of the derivations of the power equation is P = E^2/R. We know P and R and want E, so let's rearrange:

E = √(PR) and put in what we have

E = √(7.16 x 4.65) = √33.294 = 5.77 volts.