Solve the Problem $x=300,000-z / 2, y=100,000-z / 2,0 \leq z \leq 400,000$

Solve the problem.
-An investor has $400,000 to invest in stocks, bonds, and commodities. If he plans to put three times as much into stocks as in bonds, how can he distribute his money among the three types of Investments? (Let x denote the amount put into stocks, y the amount put into bonds, and z the Amount put into commodities. Let all amounts be in dollars, and let z be the parameter.)

A) $x=300,000-z / 2, y=100,000-z / 2,0 \leq z \leq 400,000$
B) $x=100,000-z / 2, y=300,000-z / 2,0 \leq z \leq 400,000$
C) $x=300,000-3 z / 4, y=100,000-z / 4,0 \leq z \leq 400,000$
D) $x=100,000-3 z / 4, y=300,000-z / 4,0 \leq z \leq 400,000$