Combinatorics question

Please provide formulas and equations.

Sam has 5 different T-shirts and three different pairs of jeans, how many different combinations can he have?

(Number of T-shirts) x (Number of Jeans) => 5 x 3=15

Explanation:
Say that the 5 different Shirts are A, B, C, D, E
And that the 3 different pairs of jeans are X, Y, Z

Sam could wear Shirt A and have the choice to wear either Jeans X, Y, or Z => 3
Same with Shirt B, C, D, E.

Therefore, it's 5 x 3=15

i hope my explanation wasn't too confusing :)

3*5 = 15.