Four items are considered for loading on an airplane, which has a capacity to load up to 25 metric ton. The weights and values of the items are provided in the table. Which items and what quantities should be loaded onto the plane so as to maximize the value of the cargo transported?

Formulate this as integer optimization model.

Item a b c d Weight (tons) 2 7 5 3 Value (per unit) 10 36 25 14