Basically, you keep going after you hit the decimal point.
You have 60 cookies to divide among 16 grandchildren.
60 ÷ 16 = 3 with a remainder of 12
To continue past the decimal point, multiply the remainder by 10 and divide it by your divisor.
12 ÷ 16 becomes 120 ÷ 16, and divided by 10 to put it in the first column past the decimal point.
120 ÷ 16 = 7, with a remainder of 8.
The first digit after the decimal point is 7.
Add another zero to the 8 to get 80
80 ÷ 16 = 5, with no remainder.
The second digit after the decimal point is 7.
So the answer is 3.75 cookies per grandchild.