Math
posted by Caitlyn .
Karen has an 86% average after 4 grades, what grade does she need to get in order to bringer average up to an 88%?

I need a formula to solve the question.... If anyone has a clue I would love it

I think its ..
a+b+c+d/4=86
86x4=344
a+b+c+d=344
a+b+c+d+e=(88x5)
a+b+c+d+e=440
440344=96
I THINK THE ANSWER IS 96 
explain how you can use multiplication to help you find 20 divide by 5

explain how you can use multdivide5 iplication to help you find 20
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20x .25