Revewing for college math placement test that expired after a year and need to retake it. so working on practice tests till i can fully be comfortable. I am horrible at math, and always have to keep relearning. It's always been my hardest subject.

"Mary has taken three tests with grades of 58%, 62%, and 64%. What does she need to score on test 4 to average exactly 68% on all four tests?"

I've tried putting the percentages in my calculator as decimals and adding them ".58+.62+.64=1.84"

I've tried putting the percentages in my calculator as decimals and dividing them ".58/.62/.64=1.461693548"

" " multiplying them ".58*.62*.64=.230144"

I know subtracting them would lead to nothing.

I've tried putting the percentages as decimals, adding them and diving by 4} ".58+.62+.64/4=1.36"

I've done "((58/100)(62/100)(64/100))/4=.46"

I can't seem to remember how to work the problem and get the right answer.

***Thank you so much for taking the time to read my post and returning any advice on my problem at hand! =D