Find the slope of the graph

How do you use the elimination method for this question? explain, because i really want to understand!

Marco has $38.43 dollars in his checking account. his checking account is linked to his amazon music account so he can buy music. the songs he purchases cost $1.29. part 1: write an expression to describe the amount of money in his checking account in relationship to the number of songs he purchases. part 2: describe what the variable represents in this situation.

The zoo collects $9.60 for every 24 tickets sold. how much will be collected for 400 tickets?