The Brainliest Answer!
Find its volume which is l×b×h then multiply with 30 and you will get the answer do you want me to show you?
1 5 1
8×6×3=144m cube than multiply it with 30 which is 4320.
ya ya I got thank u
your welcome can you mark it as the best?(brainlist)
but actually the rate is for square m
so we must find the total surface area and not the volume
Given cuboid dimensions 
Length = 8m
Breadth = 6m and
Height = 3m
Rate per m² = Rs30
Total cost = Total surface area × 30
⇒2(lb + bh + hl) ×30
⇒2[(8×6) + (6×3) + (3×8)] ×30
⇒2(48+18+ 24) ×30
∴Rs5400 is the total cost to dig the pit
but the question says Rs30 per m square not m cube 
i think its his typing mistake right valar??
but... ok check it valar
but most probably it will be m square
it can be m cube (my thinking)