The way that I would do it is turn 3/10 and 2/3 into decimals by dividing the 2 by 3 and 3 by 10
2/3 = 0.66 and 3/10= 0.3
Then multiply both by the total amount
1050 x 0.66 = 693
1050 x 0.3 = 315
Add them both together
693 + 315 = 1008
Then subtract 1008 from 1050
1050-1008 = 42