Cost is expressed by the formula tb^4. If b is doubled, the new cost R is what percent of the original cost?	Choose the correct answer:
A) r = 200  B) r = 600  C) r = 800  D) r = 1600  E) r = 50

Rationale: original cost c 1 = t 1 * b 1 ^ 4 new cost c 2 = t 2 * b 2 ^ 4 . . . . only b is doubled so t 2 = t 1 and b 2 = 2 b 1 c 2 = t 2 * ( 2 b 1 ) ^ 4 = 16 ( t 1 * b 1 ^ 4 ) = 16 c 1 16 times c 1 = > 1600 % of c 1 ans d = 1600
Answer: D