Hey there!
When we do the area of a triangle, we use the formula:
A = bh/2
With b as the base and h as the hight.
We'll get to why this formula works in a minute. If we plug in our given values into this formula, we get:
A = (5)(12)/2
A = 60/2
A = 30 feet squared
The reason why this formula works is simple. When you think of a triangle, do you ever think of it as half a rectangle? When we do the area of a rectangle, we sort of do base times height- we just do length times width. We find the area of the triangle as if it's a rectangle, and just divide it by 2 because it's half of a rectangle.
Hope this helps!