(Strip Number 6101, Original Publication Date, 13 March 1983)
Panel 1: We find Elly, Mike, Lizzie and Lawrence at Philpotts. Mike complains to Elly that Lawrence has three bucks while he only has the dollar he probably got by cleaning out the gutters or something. The tightfisted idiot who screams about opening cans by hand he calls a mother very reluctantly hands him a two-dollar bill.
Panel 2: She then thought-bubbles that she's glad that Lizzie is still satisfied with the pocket change that Mommy thinks children should be satisfied with.
Panel 3: Mike holds up a toy plane and says that he wants to get it. Elly tells him that he only has three dollars and thus cannot.
Panel 4: A baffled Mike tells her that the toy only costs $2.99.
Panel 5: Elly reminds him of something he doesn't know about: the fact that he's gotta pay sales tax.
Panel 6: Mike highlights his lack of knowledge by asking what this 'tacks' thing is.
Panel 7: Lawrence asks him "Don't you know what tax is, Mike?"
Panel 8: His explanation that it's when the govermint makes people pay more for something than what it's worth delights Elly for some reason.
Summary: The reason that Elly is happy that he said this is because it's probably what she thinks is happening. Remember, this is a woman who seems to delight in being completely incompetent to run her own financial life so an understanding of something as basic as a sales tax is sort of beyond her.