1. The problem is to multiply the numbers 4 and 5. 2. The formula for multiplication is $a \times b = c$, where $a$ and $b$ are the numbers to multiply, and $c$ is the product. 3. Applying the formula: $4 \times 5 = 20$. 4. Multiplication means adding the number 4 five times or the number 5 four times, which results in 20. 5. Therefore, the product of 4 and 5 is $20$.