make on side 0
because if ab=0 then assume a and b=0
so first minus 11r from both sides
5r²-55r+120=-30
divide both sides by 5 for convenience
r²-11r+24=-6
add 6 to both sides
r²-11r+30=0
factor
what 2 numbres multiply to get 30 and add to get -11
-6 and -5
(r-6)(r-5)=0
set each equal to 0
r-6=0
r=6
r-5=0
r=5
r=5 and 6