Given:
Amy paid $60 pair of 1 pair shorts and 2 T-shirts
Simon paid $75 for 1 pair of shorts and 3 T-shirts
Find-:
Cost of 1 pair of shorts
Explanation-:
Let 1 pair short cost is "x"
and 1 T-shirts cost is "y"
Amy paid:
Amy paid $60 pair of 1 pair shorts and 2 T-shirts
The cost of 1 pair shorts is:

So,

For Simon

So,

Solve both equation is:
eq(2) - eq(1)
Then,

So cost of 1 T-shirt is $15
For cost 1 pair short is:

So,
The cost of 1 pair of shorts is $30.