m=slope

b=y intercept

(0)=m(-4)+4

-4m=-4

m=1

y=x+4

y=mx+b, where m is the slope determined by change in y/change in x. Using 0 as the point of origin, change in y is 4. Change in x is -4. So, m=4/-4 which is m=-1. This is the slope. b is the y-intercept 4, which has been given to you. So, y=mx+b, plug in the numbers.

y=-1x+4, this is your equation.

A line is infinitely long, so plug in whatever number you like for either x or y (not both) and solve for the other (x or y). If you will notice, the only reason you were given the x-intercept is so you could figure the slope. I love math. Good luck.

find the slope using the 2 points that is m

b is easy, it is the y intecept