human
Solve one-step linear equations requiring multiplication or division, with all positive integers Isaac is solving an equation. This is the left-hand side of two lines of working from Isaac's book. Isaac always records what operation he has done to both sides of the equation.

What operation should replace the star? ![A diagram showing the change from the equations 9y = to y = represented by a gold star]() \( -9 \)
gpt
When solving an equation, subtracts instead of dividing