I need help. Also need the answer in step by step form

What is the common difference in the following arithmetic sequence? 7,3,-1,-5

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.

What is the solution to this system of equations? y= 2x - 3.5 x - 2y = -14