Answer:
25+10y
Step-by-step explanation:
The area of a rectangle is
A = l* w where l is the length and w is the width
A = 5(5+2y)
Distribute
A = 25+10y
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: 
.