Please check my work and correct if necessary. Thank You.
Using factoring and zero-product property, this is my solution for 9^2-30r+21=-4.
9r^2-30r+21=-4
9r^2-30r+25=0
(3r-5)(3r-5)=0
r=5/3
Using factoring and zero-product property, this is my solution for 9^2-30r+21=-4.
9r^2-30r+21=-4
9r^2-30r+25=0
(3r-5)(3r-5)=0
r=5/3