trying to write a formula that adds values in one column if another column
contains like values (cusip)

can't do sumif because the value changes every 2 - 10 cells or so and there
are 1400 lines in spreadsheet and about 300 cusips

I want it sum by cusip. I know there's a simple way but I've exhausted my
search.

example

cusip amt sum by cusip
912810FE3 300
912810FE3 500 800
912803BL6 100
912803BL6 200
912803BL6 300 600