Answer: $2,000
Explanation:
The amount returned was $1,980 but this amount is net of the discount of 1% that the question says they got.
The invoice amount of this return would have to account for this 1% that was given as a discount.
Assume the invoice amount is x:
1,980 = x - (1% * x)
1,980 = x - 0.01x
1,980 = 0.99x
x = 1,980 / 0.99
x = $2,000