Question

A line passes through the point (s, t) and has a slope of a. Which equation models the line?

Answer 1

So a line has this form
y=mx+b
It told in your problem that m=a since the slope is a
so we have
y=ax+b

now you know a point on this line (x=s,y=t)
plug in this point and solve for b to figure out what the y-intercept is
Replace y with t
Replace x with s
And solve for b