The number of 45 beef cattle sold is regarded as 2/3 of the unit "1", and after selling 20 cows, the number of dairy cows accounts for 2/5 of the unit "1", that is, 2/3-2/5=4/ 15, with 20 fewer cows.

It means that after selling 45 beef cattle, it will be 75.

75+45= 120