Plug in the coordinate (7, 10) into the equation so
10 = 1/2 (7) + b
You use b and not - 9 because you’re making a complete different equation so solve for b
10 = 1/2 (7) + b
Multiply 1/2
10 = 3.5 +b
Subtract 3.5 on both sides
6.5 = b
Plug b (6.5) back into the equation but flip the slope as a negative reciprocal because it’s asking for a perpendicular line so
y = -2 + 6.5 (your equation)
