She would have to score atleast a 74 on the test for her average to be 78
143 is composite. To be prime it has to have only 2 divisors i.e it's self and one but since it has 4 divisors ( 143, 1, 11 and 13) it is composite.
You are trying to solve what percent of the difference between $26.60 and $18 is of $24.60, so:
$24.60 - $18 = $6.60
24.60x = $6.60
x = 6.60/24.60
x = 0.2683
So the percent increase is 26.83%
