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 rectangular tables seat 7*10=
<gadget id="calculator">7*10</gadget>
<output>70</output>
70 pupils.
The square tables will seat 90-70=
<gadget id="calculator">90-70</gadget>
<output>20</output>
20 pupils.
The library needs 20/4=
<gadget id="calculator">20/4</gadget>
<output>5</output>
5 square tables.

<result>5</result>