Since there is no "4" added to anything in the equation "4x - 7y = 5", subtracting "4" would not be of much use:
. . . . .4x - 7y = 5
. . . . .4x - 7y - 4 = 5 - 4
. . . . .4x - 7y - 4 = 1
This doesn't isolate "y" at all.
Instead, try taking steps to get the y-term by itself. One method might be to subtract "4x" from both sides, and then divide through by "-7".
Eliz.