You're given the slope of the line and a point thru which the line passes. So it makes sense to use the point-slope form of the equation of a straight line: if the point is (a,b) and the slope is m, then
y-b=m(x-a). You'd then solve this for y to obtain the equation in slope-intercept form.
On the other hand, if you're asked to write the equation in slope-intercept form, starting with the general form of this equation may be faster: y=mx+b.
Substitute the given values for x and y (which are 25 and -9) and m (which is (2/5). Solve the resulting equation for b (the y-intercept).
Then write the finished equation: y=( ? )x + b, where b is the y-intercept you've just found.