The cost of mailing a first-class letter is $0.46 for the first ounce and $0.20 for each additional ounce or portion of an ounce. y is the total cost for mailing a letter that weighs x ounces. which type of function model would be appropriate for this situation?

If y is the total cost to mail a letter, that is what your equation should be set equal to. 
y =
Then, just to be able to send the letter, you have to pay .46 before you even weigh it.
y = 0.46 +
Finally, you can weigh your letter to determine how much more you'd have to pay (it wouldn't be fair if a 1 ounce letter and a 5 pound letter costed the same!). The problem gives you the variable for ounces, so you would do
price x ounces.

y = 0.46 + 0.20x
(I'm not sure what the name of the equation is, but it is in y = mx + b form. I believe it is "slope intercept"? That should be somewhere in your notes. Hope this helps :) )

It would be 15 m how i got the answer: (20x20) + b^2 = (25x25)400 + b^2 = 625625-400=225square that and get 15hope this : )