4x=15 (add 3 to each side),
x=15/4 (divide each side by 4),
x=3¾ (convert to mixed number, if necessary)
Another method (Do-Undo):
Remember: divide is multiply undone; add is subtract undone.
DO: 4 times x→subtract 3 from product→result is 12
Now reverse the process:
UNDO: Start with result 12→add 3=15→15 divided by 4→x=15÷4 or 15/4 or 3¾.