Question 985949
9r^2 -30r + 21 = -4
add 4 to both sides
9r^2 - 30r + 21 + 4 = 0
9r^2 - 30r + 25 = 0
factors (a perfect square) to 
(3r - 5)(3r - 5) = 0
solutions
3r = 5 twice
r = 5/3 and r = 5/3