73. If $x$ is an integer, and $y=\frac{3 x+13}{x+6}$ is an integer, then the sum of all possible values of $y$ is
Answer: 12
Solution: $y=3-\frac{5}{x+6}$, to make $\mathrm{x}, \mathrm{y}$ both integers, $x+6$ should be divisible by 5, so all possible values of $x+6$ are $-1,1,-5$, +5, the corresponding $y$ values are $8,-2,4,2$, the sum of all possible values is 12.