If there is a graph or something that you can show me, I'd be more than happy to help you.
Part a is correct.
Part b can be done a couple ways.
1) Use binomial distribution. p = 0.2, n = 144
P(x>3) = 1 - P(x=0) -p(x=1) -p(x=2) -p(x=3)
where

2) Assume a normal distribution with mean = 28.2, stdev = 4.8

Look up z-value in normal table to find probability.
Hope that helps.
Answer:
x = - 9/a + 4b/a
Step-by-step explanation:
Isolate the variable by dividing each side by factors that don't contain the variable.
-11 and 2 make the equation true.
7,000 + 200 + 50 + 6 + 0.3 + 0.05
7,256.35