Solve. {2d−e=7 {d+e=5 use the linear combination method. the solution is (3, −1) . there are infinitely many solutions. there is no solution. the solution is (4, 1).

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.

The solution is (4,1).