Equation for line passing through point and is perpendicular to the given line - (7,10), y=0.5x-9. show work

Y=mx+b
m=slope
b=y intercept
perpendicular lines have slopes that multiply to get -1

so

given
y=0.5x-9
the slope is 0.5
0.5 times what=-1?
times both sides by 2
what=-2

so the slope of the perpendicular line is -2
y=-2x+b
find b
given (7,10)
x=7 and y=10 is one solution
plug it in
10=-2(7)+b
10=-14+b
add 14 both sides
24=b
the equation is y=-2x+24

3cm and 6 and 9 cm that a possibility of that question