A = 64.4 rounded to 1 DP
b= 0.66 rounded to 2 DP
Find the maximum of a - b

127 millimeters is the answer

First step is to get rid of the square root. remember that a square root is the same as raising to the (1/2) power. see below: multiply exponents per exponent rules to get: remember you subtract exponents from the denominator and add exponents in the numerator so: simplify further: so a is the correct choice. if you don't understand this google exponent rules and it will you understand. look at the image results.