Hello from MrBillDoesMath!
Answer:
r = (v/4) (15+10y) = (5/4)v(3 + 2y)
Discussion:
To solve for "r" multiply the equation
4r/v -7=10y+8
by ( v/4).
(v/4) * ( ( 4r/v) - 7 ) = (v/4) ( 10y + 8) =>
(v/4) (4/v) * r - 7 (v/4) = (v/4) * ( 10y + 8) =>
r - 7 (v/4) = (v/4)(10y+8) => (Add 7(v/4) to both sides)
r = 7 (v/4) + (v/4) ( 10y + 8) =>
r = (v/4) ( 7 + 10y + 8 ) =>
r = (v/4) (15+10y)
Regards,
MrB