7y+3=4y-18
move 4y to the other side
sign changes from +4y to -4y
7y-4y+3= 4y-4y-18
7y-4y+3= -18
3y+3= -18
move 3 to the other side
3y+3-3= -18-3
3y= -21
divide both sides by 3 to get y by itself
3y/3= -21/3
answer:
y= -7
