Amounts spent by a sample of 50 customers at a retail store are summarized in the following relative frequency distribution.

Amount Spent (in $) Relative Frequency
0 up to 10 0.20
10 up to 20 0.40
20 up to 30 0.30
30 up to 40 0.10

The mean amount spent by customers is the closest to ________. 15) ______

A) $18.00
B) $25.00
C) $0.36
D) $20.00