If 2[3 4; 5 x] + [1 y; 0 1] = [7 0; 10 5], find (x-y).

Consider 2[3 4; 5 x] + [1 y; 0 1] = [7 0; 10 5] as shown below:
[6 8; 10 2x] + [1 y; 0 1] = [7 0; 10 5]
[6+1 8+y; 10+0 2x+1] = [7 0; 10 5]
[7 8+y; 10 2x+1] = [7 0; 10 5]
Equating the matrices we get the values of x and y as shown below:
8+y = 0 => y = -8
2x+1 = 5 => 2x = 4 => x = 2
Hence, x-y = 2-(-8) = 2+8 = 10.