GMAT Quantitative Reasoning Practice Test 3

$\mathit{X}$ is the number of guests that were supposed to show up at the party, and so Monica prepared $5\mathit{X}+2$ muffins. $\left(\mathit{X}-1\right)$ is the number of guests that did come to the party and the total number of muffins is $6\left(\mathit{X}-1\right)+3$. The number of muffins that Monica prepared is equal to the total number of muffins and so we can compare the following expressions: $5\mathit{X}+2=6\left(\mathit{X}-1\right)+3\to \mathit{X}=5$.