There is a drive that is 3/8 full => it is 1-3/8 = 5/8 empty.
The other drive is 2/5 full => it is 1-2/5 = 3/5 empty.
a) The fraction of the total amount of empty storage space is : 5/8 + 3/5 = 25/40 + 24/40 = 49/40.
b)
The first drive is : 750 x 5/8 = 468.75 gigabytes (free)
The second drive is : 750 x 3/5 = 450 gigabytes (free)
So, he has a total of 1018.75 free gigabytes left.
He will have enough space to download 150 gigabytes of data.
(If anything is wrong lmk, i'll fix it asap)