Answer:
so here tje answer is
50 <em>/</em><em> </em><em>1</em><em>0</em><em> </em><em>=</em><em> </em><em>-</em><em>k</em><em> </em>
<em>s</em><em>o</em><em> </em><em>the</em><em> </em><em>v</em><em>a</em><em>l</em><em>u</em><em>e</em><em> </em><em>o</em><em>f</em><em> </em><em>k</em><em> </em><em>=</em><em> </em><em>5</em>
Check the picture below.
now, we're assuming "to the building" means "to the ground", since we don't know the building's height, so we're also assuming the 1200m is above the building, as you see in the picture.
make sure your calculator is in Degree mode.
The C(x) equation is a parabola with a squared "x" and a positive leading term coefficient, meaning, is a vertical parabola and it opens upwards
the lowest point, or lowest cost value, it reaches, is the U-turn point, or vertex

so, the lowest cost is at