You posted another problem yesterday that looked exactly like this one.
You got a correct answer to that one, and the person who wrote the
answer told you that the volume is
Volume = (1/2) x (base of the triangle) x (height of the triangle) x (length) .
That's all you need to solve this one.
Take that same formula and plug in the numbers from this problem:
313.5 m² = (1/2) x ( 6 m ) x (height of the triangle) x (19 m)
Now simplify that equation, and you'll know the height.
It's somewhere between 5.4m and 5.8m .