Danny and Josh sell cookies at the school bake sale

Danny and Josh sell cookies at the school bake sale. For every cookie that Danny sells, Josh sells 3 cookies. Together they sell 72 cookies. How may cookies does Danny sell?

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x = number of cookies Danny sells
3x = number of cookies Josh sells {for every cookie Danny sells, Josh sells 3 cookies}

x + 3x = 72 {together they sell 72 cookies}
4x = 72 {combined like terms}
x = 18 {divided each side by 18}
3x = 54 {substituted 18, in for x, into 3x}

Danny sells 18 cookies
Josh sells 54 cookies

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