In assembling a Bluetooth device, a factory uses one of two kinds of modules. One module costs $10 and the other one, that is cheaper, costs $3.5. The factory holds a $45 worth stock of 11 modules. How many of the modules in the stock are of the cheaper kind? Choose the most appropriate option.
A) 30  B) 28  C) 25  D) 20  E) 10

Rationale: so the number of $ 3.50 modules must be 10 so that the leftover 1 modules are of $ 10 which will give a total value $ 45 . 10 * 3.50 + 1 * 10 = 35 + 10 = 45 answer : e
Answer: E