Rena buys a CD for £8.95, a book for £6.93 and a magazine for £1.97. Estimate how much she has left if she started with £40?
$${\mathtt{40}}{\mathtt{\,-\,}}{\mathtt{8.95}}{\mathtt{\,-\,}}{\mathtt{1.97}}{\mathtt{\,-\,}}{\mathtt{6.93}} = {\mathtt{22.15}} = \tiny\text{Error: }$$