4 inches = 1/3 of a foot.
The post is 3 foot, the shadow is 1/3 foot
Find the scale factor:
3 / 1/3 = 3*3/1 = 9.
The post is 9 times longer than the shadow.
This means the building is 9 times bigger than it' shadow:
105 x 9 = 945
The building is 905 feet tall.
