Solve equation I6/20

From the given examples:

• $6 (S) 2 = 3$ and $8 (S) 4 = 2$. These show that (S) represents division ($\div$).
• $5 (R) 4 = 20$ and $\frac{1}{3} (R) 9 = 3$. These show that (R) represents multiplication ($\times$). We can verify these with the combined operations:
• $3 (R) 2 (S) 4 = 3 \times 2 \div 4 = 6 \div 4 = 1.5 = 1\frac{1}{2}$. This is correct.
• $4 (R) 7 (R) 5 = 4 \times 7 \times 5 = 28 \times 5 = 140$. This is also correct.

First, perform the multiplication:

$$16 \times 20 = 320$$

Next, perform the division:

$$320 \div 4 = 80$$

The value of the expression is 80.