d+3r=39
d=r+3
(r+3)+3r=39 (Distribute r+3 with 1) Exp. 1(r) 1(3)
r+3+3r=39 (Combine like terms) Exp. r+3r=4r
4r+3=39 (Bring down -3 because the positive changes to a negative)
-3 -3
4r/4 = 36/4 (Now you bring down 4 and divide it to 36)
r=9
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So he bought 9 roses at $3 each so 9 x 3 is 27, so your answer is $27 or just 27 if this is on Plato.
