What is the value of the underline digit in 5,436,788?

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

Standard deviation of 19,29,21,22,23

Could somebody me with this radical simplification?