: Susan bought a 6-month $1,400 certificate of deposit. At the end of 6 months, she received $126 simple interest. What annual rate of interest did the certificate pay?

because they could drop even lower..

x = 3 ± √(5+y)

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).