Use a calculator and it gives you the answer right away
T= 8/100 × $8.29
t= $66.32/100
t= $0.66 rounded to the nearest penny
If she saves 2$ everyday and there are 7 days in a week, all you would need to do is multiply 2 X 7
she saves 14$ in one week
For function

we have that

. This means that period of cosine function is π. Then from the formula for period

you obtain that

and b=2.
So, the function is

. If f(0)=4, then

and, respectively, a=4.
Answer: 
.