The amount of pizza left in the pan = 3/4
Jack ate 1/2 of the pizza that was left in the pan.
Then
Amount of pizza ate by Jack = (3/4) * (1/2)
= 3/8
Now it is required to find the amount of pizza ate by Jack from the whole pizza.
Then
Amount of pizza that Jack ate from the whole = 1 - (3/8)
= (8-3)/8
= 5/8
So Jack ate 5/8 part of the total pizza. I hope this is the answer you were looking for. I have simplified the procedure for your understanding. Hope it has come to your help.