The system of equations is
2d - e = 7 (1)
d + e = 5 (5)
Create a linear combination of the equations by adding them to obtain
(2d - e) + (d + e) = 7 + 5
2d + d - e + e = 12
3d = 12
Divide by 3.
d = 12/3 = 4
From equation (2), obtain
4 + e = 5
e = 5 - 4 = 1
The solution is d=4, e=1 or (4,10.
Answer: The solution is (4,1).
