Answer:
C(x) = 
Step-by-step explanation:
Data provided in the question:
Area of the field = 3600 square feet
Fencing charges = $3.50 per foot
Let the side along the river be 'x' feet and the other side of the 'B'
now,
Area of rectangle = Bx = 3600 square feet
or
B =
feet
and total length to be fenced = x + 2B
therefore,
Total cost of fencing = Fencing charges × total length to be fenced
or
Total cost of fencing = $3.50 × ( x + 2B )
substituting the value of B from (1)
Total cost of fencing, C(x) = 
or
C(x) = 
Answer:
2a +2b +4
Step-by-step explanation:
The perimeter is the sum of the lengths of the three sides. If x represents the length of the third side, then ...
(3a +8) +(5a +b) +x = (10a +3b +12)
Subtracting from the equation everything on the left side that is not x, we get ...
x = (10a +3b +12) -(3a +8) -(5a +b)
= a(10 -3 -5) +b(3 -1) +(12 -8)
= 2a +2b +4
The length of the third side is 2a +2b +4.