the rate of toys per cereal box is the following:
[tex]\frac{2\text{ toys}}{7\text{ C. box}}[/tex]If this rate remains unchanged then for 42 cereal boxes the expected number of toys is:
[tex]\frac{2\text{ toys}}{7\text{ C. box}}\times42\text{ C. box=}12\text{ toys}[/tex]Therefore, they can expect 12 toys.