if 12 books cost $25.20, what does one book cost?

Cost of 1 book = b

$$12b=25.20$$

$$b=\frac{25.20}{12}$$

$${\frac{{\mathtt{25.2}}}{{\mathtt{12}}}} = {\frac{{\mathtt{21}}}{{\mathtt{10}}}} = {\mathtt{2.1}}$$

So one book costs $2.10

nice prices