Question 1208893
Want a B, and need average between 80 and 90
FIVE tests, only took 4 at the time


{{{80<=(68+82+87+89+x)/5<90}}}


But if instead to be last test to count as TWO regular tests, then this way:
{{{80<=(68+82+87+89+2x)/6<90}}}


You can perform the algebraic steps.