here you dont want to scale first, you need to get the full range [-5,5] if you can get it,
then you can use the mathmatical range scaling which:
to scale x form range [a-b] to range [c-d]
newX=(x-a)/(b-a) #here you will have your value in range [0-1]
finalValue=(newX*(d-c))+c #and here you will have your value in range [c-d]
which in your case if x was 2 in range [-5,5] and you need to change it to range [-450,450]
you can solve it as follows:
newX=(2-(-5))/(5-(-5)) #7/10=0.7 in range [0,1]
finalValue=(0.7*(450-(-450)))+(-450) #(0.7*900)-450=180 and thats it
hope that helps