Work Step by Step
Start with the given equation. $(x+21)+(2x+9)=90$ Combine like terms. $3x+30=90$ Subtract 30 from each side and simplify. $3x+30-30=90-30$ $3x=60$ Divide each side by 3 and simplify. $3x\div3=60\div3$ $x=20$
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