Solve two-step equations and justify each inverse operation.
Choose a direct isolation step and solve
Problem
For \(6x~-~9~=~21\), which operation should come first: A, \(\text{add}~9\); B, \(\text{divide}~by~6\); or C, \(\text{subtract}~9\)? Choose the operation that isolates \(6x\), then solve the equation.
Big Picture
What this problem is really about
Treat the left side as a product with an outside subtraction applied afterward. The direct way to isolate the product is to undo that outer subtraction on both sides; dividing too soon would leave the constant entangled with the variable term. Afterward, undo the multiplication and substitute back to check.
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