First, we calculate for all the expenses that Stewart has to pay and that is equal to the sum of the DVD price and the lunch for next week. Summing up, we get
$12.81 + $10 = $22.81
Then, we subtract this calculated value from his initial money
amount left = $26 - $22.81 = $3.19
We divide this answer by the cost of peanut per package to get the maximum number of packages Steven can buy.
$3.19 / $0.42 = 7.59
Thus, Steven can buy a maximum of 7 packages of peanut.