"The local store advertises a stereo for $1095, or $100 deposit and $32 per week for 2 years."

a) how much money does the stereo end up costing?

I have $\displaystyle 32\times 104 +100 = 3428$

b)what equivalent rate of simple interest is being changed over the 2 years?

simple interest, so $\displaystyle I= \frac{PRT}{100}$

$\displaystyle P = 1095, I= A-P = 3428-1095 = 2333, T=2$

$\displaystyle I= \frac{PRT}{100}$

$\displaystyle 2333= \frac{1095\times R\times 2}{100}$

$\displaystyle R = \frac{2333\times 100}{1095\times 2} = $ 106.53%

In the solution manual the answer is given as 117.24%