Question

30 - (8 -x) = 2y + 30
5x - 29 = x - (5-y)
DAR: X-Y

Answer 1

Primero despejas x:
30 - 8 + x = 2y + 30
x = 2y + 30 - 30 + 8
x = 2y + 8

Despejando y:
5x - 29= x - 5 + y
y = 5x -29 -x + 5
Y = 4x - 24

X-Y = 2y + 8 - 4x + 24
= 32 + 2 (4x -24) - 4x
32 + 8x - 48 - 4x
= -6 + x(8-4)

X+Y = 4x - 6

Y si quieres despejar:
Y= 3x - 6
Y = 3 (x-2)