Final answer:
There is a lack of clarity in the provided expression, which makes it difficult to simplify without additional context or clarification from the student.
Step-by-step explanation:
The expression provided by the student is (S-3)t(s-3) + (s-3)/(3-a)(st+bs-3s-3b). However, there is an ambiguity due to possible typos and the lack of clear grouping of terms or use of parentheses. If we assume the student meant (S-3)t and (s-3) are to be multiplied and then added to the fraction (s-3)/((3-a)(st+bs-3s-3b)), the resulting expression simplifies depending on the relationship between 'S' and 's', and the values of 'a', 't' and 'b'. Without specific values, the expression cannot be simplified further. If the variables mentioned have other specific values like in the information provided, these would be plugged into the expression to obtain a numerical result, but as of now, the provided snippets of information don't seem to be directly related to the given expression. To correctly solve this, more context or clarification from the student would be needed.