(X+5)(x-3) Find the product

There is a line with slope 1/a going through the point (a, a²). find the equation of the line perpendicular to this line at this point. (don’t let this problem intimidate you! solve the problem as you would if i’d given you specific values. just use variables instead.)

Isee the amount was $90.00 then reduced to $75.00 , what is the percent ?

How do i do this? i don’t understand