Answer:
r = - [tex]\frac{St}{S-t}[/tex]
Step-by-step explanation:
Given
S(r + t) = rt ← distribute parenthesis on left side
Sr + St = rt ( subtract rt from both sides )
Sr - rt + St = 0 ( subtract St from both sides )
Sr - rt = - St ( factor out r on the left side )
r(S - t) = - St ( divide both sides by (S - t)
r = - [tex]\frac{St}{S-t}[/tex]
