You can put this solution on YOUR website! A. (2r-3s)(5r+7s)
Using FOIL (First-Outers-Inner-Lasts)
Take FIRSTS; (2r)*(5r)
10r^2 (note it is r-squared, becuase, r*r is r^2; this is a common error, so watch out!)
Take OUTERS: (7s)*(2r)
14rs
Take INNERS: (-3s)(5r)
-15rs
Then, ADD the outers and inners (because they are "like terms" in an equation, you MUST SIMPLIFY)
You get... 14rs + -15 rs = -(1)rs or just -rs
Take LASTS: -3s*7s
-21 s^2 (another "squared" to watch out for!)
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