How do you do this? i am so stuck!

If you watch YouTube it would better break it down for u

X⁴+ax³+ax²+11x+b=0    

for x=3
3⁴+a*3³+9a +11*3+b=0
81+27a+9a +33+b=0
36a+b+114=0

for x=-2
(-2)⁴+a*(-2)³+(-2)²a+11*(-2)+b=0
16-8a+4a-22+b=0
-4a+b-6=0

system
36a+b+114=0
-4a+b-6=0

subtract second equation from first
36a+b+114+4a-b+6=0
40a+120=0
40a=-120
a=-3,
-4a+b-6=0, -4*(-3)+b-6=0,  12-6+b=0, b=-6