A box has exactly 100 balls, and each ball is either red, blue, or white. If the box has 5 more blue balls than white balls, and thrice as many red balls as blue balls, how many white balls does The box has ?  Choose the correct option.
A) 8 B) 10 C) 12 D) 14 E) 16
x = the number of red balls   y = the number of blue balls   z = the number of white balls   From the first sentence we have   Equation #1: x + y + z = 100   ...the box has 5 more blue balls than white balls...   Equation #2: y = 5 + z   ...thrice as many red balls as blue balls...   Equation #3: x = 3y   Solve equation #2 for z: z = y - 5   Now, we can replace both x and z with y in Equation #1   3y + y + (y - 5) = 100   5y - 5 = 100   5y = 105   y = 21   There are 21 blue balls. This is 5 more than the number of white balls, so z = 16. That's the answer. Just as a check, x = 63, and   63 + 21 + 16= 
<gadget id="calculator">  63 + 21 + 16</gadget>
<output>100</output>
100.   Answer= 16,(16)
<result>E</result>
A box has exactly 100 balls, and each ball is either red, blue, or white. If the box has 5 more blue balls than white balls, and thrice as many red balls as blue balls, how many white balls does The box has ?