At the end of the month, a certain ocean desalination plant’s reservoir contained 30 million gallons of water. This amount is twice the normal level. If this amount represents 75% of the reservoir’s total capacity, how many million gallons short of total capacity is the normal level?
Select the correct option
A) 10  B) 15  C) 20  D) 25  E) 30
the Q talks of total capacity, normal level, present level, shortage etc..   so it is all about not going wrong in these terms   30 MG= 75% of Total..   total = 30/.75= 
<gadget id="calculator">30/.75</gadget>
<output>40</output>
40MG..   Normal level= 1/2 of 40=20MG..   shortage of normal level=40-20= 
<gadget id="calculator">40-20</gadget>
<output>20</output>
20MG..   20
<result>C</result>
At the end of the month, a certain ocean desalination plant’s reservoir contained 30 million gallons of water. This amount is twice the normal level. If this amount represents 75% of the reservoir’s total capacity, how many million gallons short of total capacity is the normal level?