To round each number to the nearest tenth, we have to look at the second digit after the decimal point, the hundredths. We look at tenths to round whole numbers, hundredths to round tenths, thousandths to round hundredths, etc. If the digit is 4 or below, then we would round down. If the digit is 5 or up, we would round up.
11.14
The digit is below 5, so we round down to 11.1.
9.543
The digit is also below 5, so we round down to 9.5.
Henceforth, adding these two numbers, we can conclude that an accurate estimation of the sum is 11.1 + 9.5, or 20.6.
If we wanted to round this answer further, we would use the same rounding rule. 20.6, where the tenths place digit, 6, is above 5, would be rounded up to 21.