Answer
See below.
Work Step by Step
If Scott gets $x$, then Alice gets $0.75x$ and Tricia gets $0.5x$, thus our equation is: $x+0.75x+0.5x=900000\\2.25x=900000\\x=400000$.
So Scott gets $400000$, Alice gets $0.75\cdot400000=300000$ and Tricia gets $0.5\cdot400000=200000$