I don't no how to start this problem and solve it, Can someone help me with this problem please

x^3-4x^3-6x+24

Find the equation of the line that passes through the points (1,3) and (3, -5)

I did the second one and I got y= -x-2 and I want to c if this is answer is correct and also I still have trouble solving the first problem x^3-4x^3-6x+24

-3x^3-6x+24

then solve x and graph to check.