How many of Part D should it order?

Question

For every one of Part A a company orders, it also needs to order four of Part B, three of Part C and nine of Part D.  If the company orders 28 of Part B, how many of Part D should it order?

 

(The answer choices are:  58, 63, 68. 70, 84)

Answer 1

we can see that for every 4 parts of B we need 9 parts of D,

so if we order 28 parts of B,we should get the required parts of D by the equation  4/28=9/x 

so x =63

Answer 2

For every part A you oder 9 part d's.  We know how many part B's so lets see how many part A's we have 28-4=7.  Thee are 7 part A's.  Thus, we can multiply by 9 and that gives us 63 part D's.