Itook one picture of a math question, here take a look.

To solve this question, we have to set up a proportion that relates the two triangles.

In the bigger triangle, the bottom piece equals 30 feet.
In the smaller triangle, the bottom piece equals 5 feet.

In the bigger triangle, the height equals x feet.
In the smaller triangle, the height equals 30 feet.

In a proportion, this would be:

5/30 = 30/x 

To solve this proportion, we can use cross-products, or setting the products of the opposite numerators and denominators equal to each other.

5 * x = 30 * 30

Now we have to simplify both sides of the equation by completing the multiplication operations.

5x = 900

Finally, we must divide both sides by 5, to get the variable x alone on the left side of the equation (get rid of coefficient of 5)

x = 180

Therefore, x = 180 or the height of the bigger triangle (building) is 180 feet.