Answer:
Step-by-step explanation:
1. Y varies jointly as R and T
Y = k*R*T
Y = kRT
Where,
k = constant of proportionality
2. B is directly proportional to the square of A and inversely proportional to the cube of C.
B = k(A²) / C³
B = kA²/C³
Where,
k = constant of proportionality
the answer is 0.2 or one fifths
One of the product rules for exponents was used.

Or, you can consider that the definition of an exponent and the associative and commutative properties of multiplication were used.
5x[$25.85-($25.85 x 0.10) ] + (5 x 2.50)=$128.83 compared to[ 5 x 27.36( $27.36 x 0.15)]+ 10.00= 126.28 is the least amount.
answer is ------> $126.28