Why is it to estimate the answer before adding or subtracting decimals?

Suppose that 15 inches of wire cost 60 cents. at the same rate, how much (in cents) will 12 inches of wire cost

Jan accidently ran 7 minutes longer than he was supposed to. write an expression for the total amount of time jan ran if she was supposed to run m minutes

Can you me with this question? i'll reward *30 points i just need with this one question so that i could solve the others. * edit: i originally set up the question to reward 30 points, but for some reason i can only reward 15. if you don't get 30, then i'm sorry. i'm still kind of new to this site