You have two u. s. coins that add up to 30 cents. one of them is not a nickel. what are the two coins?

There are 4 different US coins...
One is a quarter, which equals to 25c.
One is a dime, which equals to 10c.
One is a nickel which equals to 5c. 
And the last one is a penny which equals to 1c.

You have two coins that equal 30c.
You can't use a dime, so you must use 2 quarters, 2 dimes, 2 pennies, a quarter and a penny, a quarter and a dime, or a dime and a penny. 

2 quarters = 50c.
2 dimes = 20c.
2 pennies = 2c.
a quarter and a penny = 26c.
a quarter and a dime = 35c.
and a dime and a penny = 11.

So it's kinda impossible for two US coins (other than a nickel) to equal 30c. 
Good luck though!
. 

Let the two coins be x and u,

the total is .30 so it should be .25 + .5

25 cent is a quarter and 5 cent is a nickel.

Yes, that is the correct formula. to solve this problem given the number of years, plug in the number of years for t and plug the whole thing into the