I have 6 columns and many rows in a spreadsheet i want to create a formula
that looks at two common columns and if the same replace a column with an
amount from another column. Below is sort of an example of what I mean:

column a column b column c column d column e column f
acc50138 ACCCS20-1 6.14 acc50138 acccs20-1 10.00
acc50140 Prevention 31.05 acc50269 RTU 15.00
acc50379 concentrate 5.00 acc50379 concentrate 5.00

so what i need is the formula to look at column a and d if they are the same
then replace column c with the amount of column f. Any suggestions?