Step-by-step explanation:
last week there were 19+30+77 = 126 customers.
19/126 = 1/14 paid cash.
30/126 = 5/21 paid by debit card.
77/126 = 11/18 paid by credit card.
next week he expects 1800 customers.
that is compared to 126 a factor of
1800/126 = 300/21 = 100/7
now we actually only need to apply the same factor to any part of the total sum to get their share in the new total sum.
it simply follows the rule
(a + b + c) × d = ad + bd + cd
so,
77 × 100/7 = 11 × 100 = 1100 customers are expected to pay per credit card.
