We can estimate the division by rounding the digits to nearest tens ,hundreds .
The digits given are 868 and 28.
The general rule tells us to look at the digit to the right of the digit we want to estimate, if it is less than 5 then we round down, and if it is greater than 5 we round up.
In the digit 868 we round it to nearest hundred the digit is greater than 850 so it is rounded up to nearest hundred that is 900.
The digit 28 is rounded to nearest tens .The digit is greater than 25 so it is rounded up that is 30.
The best choice for estimating is B. 900 ÷30