Question 894562
You may draw a figure of two triangles sharing a side y, a vertical length of the building.  from bottom of y, x to the right is the angle of elevation 83.74; and continuing 24 more to the right, that point is at the angle of elevation 79.63.


This figure as described (and labeled) will give you these two equations.


{{{highlight_green(y/x=tan(83.74))}}} and {{{highlight_green(y/(x+24)=tan(79.63))}}}.


Solve each of these for x, and then equate the two expressions; so that you have one equation in the single variable, y.  Now you can just solve for y, the height of the building.