A: What decimal is equivalent to 72/100? Well, 72/100 means you have 72 out of 100. Meaning it's not a whole number, so this means as a decimal, your answer would be behind the decimal point. Behind the decimal, you have 3 main places. Tenths, Hundredths, and Thousandths. It goes much further than that, of course, but most don't have to worry about those. 72/100 is represented as 72-hundredths, or .72 You are correct.
B: .72 as a fraction is 72/100. Simply divide by 2 until you simply can't anymore, this saves you time. 72/100 divided by 2 equally is 36/50. This divided by 2 equally is 18/25. This is the lowest form, you are correct.
C: Well, also simple. We know that when you have an exponent, you multiply the number by itself. 9^2 is 81, because 9*9=81. HOWEVER, this applies to only positive exponents. With negative exponents, you have to make it a fraction as 1. So, your answer is indeed 1/81
