I don’t get this type of problem

Aswim teacher sells lesson packages. the best deal has the highest ratio of lessons to total cost.swim lesson packagesnumber of lessons total cost$10$4010 1 $8015$80which package is the best deal? l lesson for $105 lessons for $4010 lessons for $8015 lessons for $80mark this and returnsave and exit

Whats the name of the vertical axis

If t17 = 3 (t5) in an arithmetic progression, find t1 in terms of d.