Question

Turn into slope intercept form

a = 400 - 2b

a = b + 100

Answer 1

Suppose a is the independent variable,
we know that slope intercept equation for a line with slope m and y-intercept c is
y=mx+c

here we have a=400-2b
or
2b=400-a
divide both sides by 2
b=-a/2+200
here slope is -1/2 and intercept of 200

now you try the second part
bring b to one side, making sure that its coefficient is +1
you'll have equation in the form
b=ma+c