<PRE><B>Question 123017</B>
Let x = grade on fourth exam

{{{ (84+84+84+x)/4=85}}}


Mult both sides by 4:
{{{ 84+84+84+x=340}}}
{{{252+x=340}}}

{{{x=340-252=88}}}


R^2


P.S.  An easier way to do this is to realize that if you need an 85 average, and your grades are below 85 by 1 point on each of 3 exams, then you need an 85 on the last test, plus 3 points (to make up the shortfall on the first 3 exams), for a total of 88.

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