Use the sample above to answer questions 21 to 25.

Based on the sample operations:

• $6 (S) 2 = 3$ and $8 (S) 4 = 2$ indicate that (S) represents division ($\div$).
• $5 (R) 4 = 20$ and $\frac{1}{3} (R) 9 = 3$ indicate that (R) represents multiplication ($\times$).
• The combined operation $3 (R) 2 (S) 4 = 1\frac{1}{2}$ means $3 \times 2 \div 4 = 6 \div 4 = 1.5$, which confirms the interpretation.
• The combined operation $4 (R) 7 (R) 5 = 140$ means