Will rounding to the nearest 10 or 100 give a closer estimate of 748-431?

The pyramid below was dissected by a horizontal plane which shape describes the pyramid horizontal cross section

In the diagram, a building cast a 35-ft shadow and a flagpole casts an 8-ft shadow. if the the flagpole is 18 ft tall, how tall is the building? round the the nearest tenth.

28 x 12 + 34 = ? it's for a test that if i fail on i will not proceed into the honor roll society i always dreamed of!me! worth 50 !