How many calories should be eaten by a 20 years old female?

I read an article that said the following.. women: If you are 5' tall you should weigh 100lbs for every inch over 5" add 5lbs Measure your writst if it is less than 6" subtract 10% from the weight you just calculated. If it is 6" it stays the same, if it is more than 6" add 10%. If you are totally inactive (no exercise) multiply the weight calculated by 11, If you exercise regularly (2-3 times a wk) multiply by 13, if you exercise 4-5 times per wk multiply it by 15, and if you exercise 6-7 times a wk multiply it by 18. That is the number of calories you should intake daily ex. 5'4 woman w/ 6" wrist= 120lbs, exercises 2-3times/ wk= 1560calories. To find out grams of fat multiply by .20 1560*.20= 312 1g of fat= 9calories 312/9= 35grams/day