What is the surface area of this figure?

The function show two sisters' savings account and the rate at which they plan to deposit money

3.4a=57.8 what is the the value of a

Long division setup showing an incomplete calculation. 12 is in the divisor, 6839 is in the dividend, and 5 hundreds and 6 tens is written in the quotient. 6000 is subtracted from 6839 to give 839. an unknown value represented by a box is being subtracted from 839. what number should be placed in the box to complete the division calculation?