Question 1196964
.
<pre>

x = score on the final exam.


Your equation is, OBVIOUSLY,

    {{{(x+(x+5) + (x+13))/3}}} = 90.


Simplify and find x

   x + (x+5) + (x+13) =270

   3x = 270 - 5 - 13 = 252.

    x                = 252/3 = 84.    <U>ANSWER</U>    (The typo is just fixed - thanks to tutor @greenestamps)
</pre>

Solved, with full explanation.