SATMathematics Practice Test 1

since $\mathit{k}=3$,one can substitute 3 for k in the equation $\frac{\mathit{x}-1}{3}=\mathit{k}$,which gives $\frac{\mathit{x}-1}{3}=3$.
Multiplying both sides of $\frac{\mathit{x}-1}{3}=3$ by 3 given as $\mathit{x}-1=9$ and then adding 1 to both sides of $\mathit{x}-1=9$ and then adding 1 to both sides of $\mathit{x}-1=9$ gives $\mathit{x}=10$
Choices A, B, and C are incorrect because the result of subtracting 1 fromthe value and dividing by 3 is not the given value of k, which is 3.