Step 1 :Let the amount invested in the 7\% account be \(x\) and the amount invested in the 8.5\% account be \(y\).
Step 2 :Write the system of equations: \(\begin{cases} x + y = 900 \\ 0.07x + 0.085y = 73.50 \end{cases}\)
Step 3 :Solve the system of equations to find the values of \(x\) and \(y\).
Step 4 :\(x = 200\) and \(y = 700\)
Step 5 :\(\boxed{\text{Sullivan invested }\$200\text{ in the 7\% simple interest account and }\$700\text{ in the 8.5\% simple interest account.}}\)