What is the solution? 21=42−3r r=−8 r=−7 r = 7 r = 8

R=-7, you have to put each answer in the equation, therefore; 21=42-3(-7) So you have to do multiplication (PEMDAS, if you arent aware of that acronym then it stands for the order of what to do with an equation, Parentheses get solved first, then Exponents, then multiplication, then division, then addition, then finally subtraction. Solving in that order will solve your answer correctly.) With -3 times -7 which gives you 21. Then you do 42 - 21 which equals 21. So 21 = 21.