Question

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Answer 1

Just wondering for clarification, is it just the xy in the numerator of the fraction or rst+xy all in the numerator?

Answer 2

all in the numerator

Answer 3

Given:\[s=\frac{ rst + xy }{ ty-r }\]Solving:
\[s(ty-r)=rst+xy\]\[s(ty-r)-rst=xy\]\[sty-sr-rst=xy\]\[-sr-rst=xy-sty\]\[sr+rst=sty-xy\]\[r(s+st)=sty-xy\]Therefore:
\[r=\frac{ sty-xy }{ s+st }\]