Let x be the number of bagels Arnie sold. We have the following equation:

0.30(x - 4) - 0.20(4) = 2.40

Distribute and simplify:

0.30x - 1.20 - 0.8 = 2.40

Combine like terms:

0.30x - 2 = 2.40

Add 2 to each side:

0.30x = 4.40

Divide each side by 0.3

**x = 14.67 ~ 15**