Question 946578
Name the variables : Three pieces A, B, and C.
{{{A+B+C=200}}}
{{{B=3A}}}
{{{C=2B=2(3A)=6A}}}
Now you have three independent equations with three unknowns. 
You can solve it.
{{{A+B+C=200}}}
Substitute,
{{{A+3A+6A=200}}}
Now solve for A.
Then go back and solve for B and C. 
Repost if you get stuck and need more help.