If we let X represent the number of pounds of coal that the blue boxcar can hold, then 4000=(1/2)X.
Solving for X, we get X=<<8000=8000>>8000 pounds of coal, which represents what the blue car can hold.
Thus, the red boxcar can hold 3*8000=<<3*8000=24000>>24,000 pounds of coal.
3 red boxcars can carry 3*24,000=<<3*24000=72000>>72,000 pounds of coal.
7 black boxcars can carry 7*4,000=<<7*4000=28000>>28,000 pounds of coal.
4 blue boxcars carry 4*8,000=<<4*8000=32000>>32,000 pounds of coal.
Together, all the trains boxcars can carry 72,000+28,000+32,000=<<72000+28000+32000=132000>>132,000 pounds of coal.
#### 132,000