If x and y are positive integers such that y is a multiple of 5 and 3x + 4y = 600, then x must be a multiple of which of the following?  Pick.
A) 3.	B) 6.	C) 7.	D) 8.	E) 10.
If y is a multiple of 5, then 4y is also a multiple of 5.   3x = 600 - 4y   600 - 4y is even and it is a multiple of 5.   Thus x must also be even and a multiple of 5.   Therefore x must be a multiple of 10.   The answer is 10..
<result>E</result>
If x and y are positive integers such that y is a multiple of 5 and 3x + 4y = 600, then x must be a multiple of which of the following?