.
x + y = 25, (1)
2x - 1 = 4y +1. (2)
From equation (1, express u = 25-x and substitute it into equation (2).
You will get a single equation for one unknown
2x - 1 = 4*(25-x) + 1.
Simplify and solve for x:
2x - 1 = 100 - 4x + 1,
2x + 4x = 100 + 1 + 1,
6x = 102 ====> x =
= 17.
Answer. x = 17, y = 25-17 = 8.
Solved.