What does it mean for a product of factors to be expressed using exponents

Exponential form is when you expressed the product of the factor in an exponent.
By this, you make your equation shorter.
For example:
The product of the factor is 4, then you express it using exponent. That becomes 2^2
=> 2^2 = 2 x 2, which is equals to 4
Next, the product of the factor is 256, then you express it using the exponent. It becomes 2^8
=> 2^8 = 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2, which is equals to 256

The correct answer is -20y