Question 122206
cost of making each day's batch of N doughnuts=C=30+0.1N
cost of making each day's batch of N+20 doughnuts=C=30+0.1(N+20)
Increase in cost ( step2-step1=30+0.1(N+20) minus 30+0.1N
=30+0.1N+(0.1*20)-30-0.1*N
=30+0.1N+2-30-0.1N
30and -30 cancel
0.1N and -0.1N cancel
Leaving 2 as remainder

So Additional cost  =2 Dollars
The batch cost will increase by only 2 dollars
okay