Here, consider c as variable and x as constant.
3(x + c) - 4y ≥ 2x - 5c
3x + 3c - 4y ≥ 2x - 5c
3x - 2x - 4y ≥ -5c -3c
x - 4y ≥ -8c
8c ≤ 4y - x
c ≤ (4y - x)/ 8.