Step-by-step explanation:
See drawing
Using V= I * resistance
v = (.025 A) * (r+400 Ω) <====given
and
v = (.060A) * ( r+100 Ω)
equate the two equations
.025(r + 400) = .060(r+100) <==== solve for r = 114 .3 Ω
then use this value in either of the equations to calculate v = 12.9 v