The expression for (r-s)(x) is found by subtracting s from r. That difference is

. The expression for (r+s)(x) is found by adding them, which is

. Now we are told to evaluate (r*s)(x) which means they want us to multiply those and state the "new" expression that results.

. There you go!
Use the compound interest formula.
A = P*(1 +r/n)^(n*t)
where P is the principal, r is the annual rate, n is the number of compoundings per year, and t is the number of years.
For the first investment, ...
A = 208,000*(1 +.08/4)^(4*5) = 309,077.06
For the second investment, ...
A = 218,000*(1 +.07/2)^(2*4) = 287,064.37
Totaling both investments at maturity, Megan has $596,141.43.
The volume is V≈678.58cm³