CAN ANYONE HELP ME? :)

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.

Someone me what is the area of this figure? 18m 18m 8m 16m