Straight Lines and Pair of Straight Lines

Let $\mathrm{A}(-1,1)$ and $\mathrm{B}(2,3)$ be two points and $\mathrm{P}$ be a variable point above the line $\mathrm{AB}$ such that the area of $\triangle \mathrm{PAB}$ is 10. If the locus of $\mathrm{P}$ is $\mathrm{a} x+\mathrm{by}=15$, then $5 \mathrm{a}+2 \mathrm{~b}$ is :