Simplify using appropriate identity 0.85 × 0.85 +2 × 0.85 ×0.15 × 0.15

Remember that multiplication is to be done before addition or subtraction.  We see that both terms have the factor 0.85:

0.85 × 0.85 +2 × 0.85 ×0.15 × 0.15 =

0.85 * ( 0.85 + 2*0.15*0.15).  

This is equivalent to 0.85 ( 0.85 + 2*0.0225 ) = 0.85 ( 0.895 ).

This last result could be left as is, or evaluated with a calculator:

0.76075

the revenue of the fitness center, y, is the product of two factors: the number of members and the fee paid by each member. there are 320 members now, but number of members goes down by 10 for each $5 increase in fees, so if x is the number of $5 price increases then members is equal to (320 - 10x). since the fee is currently $45, and the fee increases by $5 for every price bump x, the fee is given by (45 + 5x). so, revenue y is given by y = (320 - 10x)(45 + 5x).