Pleaaaseee explaiiin: (there's a picturee)

"Proportionality Theorem" compares the sides of the same triangle 
Here, According to that theorem, 
ST / RS = UT / PU

If FG is an altitude, then <DFG  is an right triangle.
In short, Your Answer would be Option B

For last question here, remember, longest side must be greater than either side, and must be smaller than sum of those smaller sides.

1. 0.3 •4 is the same as 4 groups of 0.32. 7•0.8 is the same as 7 groups of 0.83. it increases by 0.5 every time, so 0.5x4 it increases by 0.9 every time, so 0.9x5. 0.9•12=10.86. 0.47•5=2.35i can finish the next ones in a separate post