Given the stream of consciousness rationale, provide a reasonable question and answer. Rationale: The rectangular tables seat 7 * 10 = 70 pupils. The square tables will seat 90 - 70 = 20 pupils. The library needs 20 / 4 = 5 square tables.
 The question and answer:
A library has 7 rectangular tables and the remaining tables will be square tables. A rectangular table seats 10 pupils while a square table seats 4 pupils. How many square tables are needed so that 90 pupils can read at the same time?
The answer is 5