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 $6. The factory holds a $80 worth stock of 12 modules. How many of the modules in the stock are of the cheaper kind?  Choose the correct choice from the following options:
A) 20
B) 25
C) 10
D) 30
E) 35
So the number of $6 modules must be 10 so that the leftover 2 modules are of $10 which will give a total value $80. 10*6+2*10 = 60+20= 
<gadget id="calculator">60+20</gadget>
<output>80</output>
80   Answer : 10
<result>C</result>
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 $6. The factory holds a $80 worth stock of 12 modules. How many of the modules in the stock are of the cheaper kind?