Final answer:
The two-step equation in the given options is 2x + 9 = 21. It involves using inverse operations to isolate the variable and solve for its value.
Step-by-step explanation:
A two-step equation is an equation that requires two separate steps to solve. It involves using inverse operations to isolate the variable. In the given options, the two-step equation is 2x + 9 = 21. The first step would be to subtract 9 from both sides of the equation, giving 2x = 12. The second step would be to divide both sides by 2, which gives the solution x = 6.
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