Hey there! :D
6 3/4 - 1 2/3
We can convert the fractions to decimals, and if the decimals are bigger than .5, we can round up to the nearest whole number.
3/4= .75 <== we can round up to the nearest whole number
6.75= 7
2/3= .66666 <=== we would also round this up to the nearest whole number
1.66666= 2
7-2 <=== estimated expression
I hope this helps!
~kaikers