Circuit equations problem.

Consider the circuit of Figure:

By mesh-current method, find the total power developed in the circuit.


Loop 1:
-125V + 2(I1 - I2) + 3(I1 - I3) + 75V = 0

Loop 2:
2(I2 - I1) + 7I2 + (I2 - I3) = 0

Loop 3:
-75V + 3(I3 - I1) + (I3 - I2) - (0.5v∆) = 0


v∆ = 2(I1 - I2)
Substitute into equation loop 1.

P= VI
Total power developed in the circuit:
= (125V ?- I1) + (75V ?- (I3 - I1))

Izzit doing in this way? Correct me if i m wrong. I m not sure about the three loop equations above.