The situation described is shown in the following picture:
To find the height of the balloon from the ground we first need to find x. From the figure we notice that we have a right triangle and that we want the opposite leg of this triangle. If we remeber the definition of the tangent function:

then we have in this case:

Now we add the value of x to the height of the building:

Therefore the height of the balloon is 1514.8 ft