If $2x+3y=46$ and $3x+5y=74$, then the value of $5x+8y$ is:

Adding the two equations term by term gives $5x+8y=46+74=120$ straight away — no need to find $x$ and $y$ at all. (Subtracting instead gives $x+2y=28$.) For confirmation, solving properly gives $x=8$ and $y=10$, and $5(8)+8(10)=120$.