Posted by Carlos on Saturday, July 2, 2011 at 4:11pm.
(5+x)(6+x) = 3*30 = 90
30 + 11 x + x^2 = 90
x^2 + 11 x - 60 = 0
(x+15)(x-4) = 0
x = 4
check
9*10 = 3*30 yes
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