Question 1055597
Your problem setup is a little disjointed. 
14 people sat on a test and got a 68% average, then one more person took the test and got an 83%?
I'm assuming that's what you mean.
If not repost and explain it better.
The average, A, is
{{{A=68}}}
It's the total of all scores divided by 14,
{{{T/14=68}}}
{{{T=14*68}}}
Now add the new test scores,
{{{T[new]=14*68+83}}}
So then the new average will be the new test scores divided by 15,
{{{A[new]=(14*68+83)/15}}}
Use your calculator to complete.