all of the numbers on the right-hand of the equal (=) sign are meant to be read as decimal numbers. We have not always shown the decimal subscript on such expressions as 3(81). But
310(8110)
is a complicated way of saying it. You’ll have to remember that if no subscript is shown, the number is meant to be read as a decimal number.
Now, we can get to the conversion from decimal to octal fractions after we clear up one more little point.