The answer is D I think
Given the 2 equations
2x + 5y = 21 → (1)
x + y = 3 → (2)
Rearrange (2) expressing y in terms of x, by subtracting x from both sides
y = 3 - x ← Substitute into (1)
2x + 5(3 - x) = 21 ← distribute and simplify left side
2x + 15 - 5x = 21
- 3x + 15 = 21 ( subtract 15 from both sides )
- 3x = 6 ( divide both sides by - 3 x = - 2 → D
X=-2