If $3 r=18$, what is the value of $6 r+3$ ?
SAT · Math · previous-year question
- A.6
- B.27
- C.36
- D.39correct
Answer
D. 39
Explanation
Choice D is correct. Dividing each side of the equation $3 r=18$ by 3 gives $r=6$. Substituting 6 for $r$ in the expression $6 r+3$ gives $6(6)+3=39$.Alternatively, the expression $6 r+3$ can be rewritten as $2(3 r)+3$. Substituting 18 for $3 r$ in the expression $2(3 r)+3$ yields $2(18)+3$, or $36+3=39$Choice A is incorrect because 6 is the value of $r$; however, the question asks for the value of the expression $6 r+3$. Choices $\mathrm{B}$ and $\mathrm{C}$ are incorrect because if $6 r+3$ were equal to either of these values, then it would not be possible for $3 r$ to be equal to 18 , as st
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