1) 15 out of 48 used credit cards so the probability would be:
15/48 = 5/16 = 0.3125 = 31.25%
Now you multiply that by the amount of people:
2400 x 0.3125 = 750
You can expect 750 people to use a credit card.
2) 9/600 = 3/200 = 0.015 = 1.5%
5000 x 0.015 = 75
75 are expected to be defective locks.
3) 294/1400 = 21/100 = 0.21 = 21%
25000 x 0.21 = 5250
You would expect 5250 to be returned.