I think that you multiply 2 with 4 to get 8 and then multiply 8 with 7 to get that number then add 2.75... to get the total.
Hope it helped..
You can get the number by dividing 19.2 by 0.40
The number is 19.2/0.40 = 48
You can add 7+3 then add 9 ad you get 19
