Perpendicular lines have a slope that is the opposite reciprocal of the given slope. This means the new slope is -2.
Then you plug in the point to get your new y intercept 10=(-2)7+b
You solve by first multiplying -2 and 7 to get 10=-14+b
Then you add 14 on both sides to get 24=b
You plug this into the equation with your new slope to get y=-2x+24
