Answer:
1.6
Step-by-step explanation:
You want the solution to ...
[tex]5x+7=\dfrac{1}{3}(61-10x)\\\\3(5x+7)=61-10x\\\\25x=40\qquad\text{add $10x-21$}\\\\x=\dfrac{40}{25}\\\\\boxed{x=1.6}[/tex]
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Check
5(1.6)+7 = 15
61 -10(1.6) = 45
15 is 1/3 of 45 as required.