When changing a decimal to a fraction, it helps to read it aloud.
0.45 is "45 hundredths" which means the same thing as 45/100. What remains is to reduce this fraction if possible; that is, try to find a common factor between both the numerator and denominator and divide each by that factor. Here, 45 and 100 are both divisible by 5, so 45/100 = 9/20.
9 and 20 have no common factors, so this is your answer in lowest terms.
0.45 is "45 hundredths" which means the same thing as 45/100. What remains is to reduce this fraction if possible; that is, try to find a common factor between both the numerator and denominator and divide each by that factor. Here, 45 and 100 are both divisible by 5, so 45/100 = 9/20.
9 and 20 have no common factors, so this is your answer in lowest terms.