We get minimum achievable average waiting time using SJF scheduling.
Lets just name these processes for explanation purpose only as $A = 16, B = 20$ and $C = 10.$
Order them according to burst time as $C<A<B$
C will not wait for anyone, schedule first ( wait time = 0)
A will wait for only C (wait time = 10)
B will wait for both C and A (wait time = 10 + 16)
Average wait time = $ \frac{0+ 10 + (10+16)}{3} = \frac{36}{3} = 12. $
No need to make any table or chart.
This is all for explaining purpose, you can actually ans this within 10-15 sec after reading the complete question.