Piper skated to the park and then walked to the store. He skated 2 times as long as he walked. The total time spent walking and skating was 21 minutes. Write an equation that can be used to solve for how long it took Piper to walk from the park to the store?
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x + 2x = 21
x + 2 = 21
1/3x = 21
1/2x + x = 21
