Question 260824
{{{(80+76+87+X)/(100+100+100+200)=80/100}}}
{{{80+76+87+X=400}}}
{{{243+X=400}}}
{{{X=157}}}
Since the final test is out of 200, 
{{{157/200=Y/100}}}
{{{Y=78.5}}}
You need to get at least a 78.5 on the final to get a B.