Suppose a Consumer Has Preferences Over Two Goods, X and Y

Suppose a consumer has preferences over two goods, X and Y, which are perfect substitutes. In particular, two units of X is equivalent to one unit of Y. If the price of X is $1, the price of Y is $3, and the consumer has $30 of income to allocate to these two goods, how much of each good should the consumer purchase to maximize satisfaction?

A) 30 units of X and 0 units of Y
B) 0 units of X and 10 units of Y
C) 15 units of X and 5 units of Y
D) 15 units of X and 0 units of Y