Question 143416
To combine 3x and 2x-1 you must first combine "like terms". The like terms would be  3x and 2x. 
3x + 2x = 5x
You also have a -1 left over. Since -1 does not have any like terms, you would leave it.
The answer would just be: 5x-1

Just in case you have some confusion: 
a monomial is a single term hense "mono- meaning one"such as 6x or 10y

a binomial has two terms hence "bi- meaning two" such as  2y + 5 or 7x + 3

Hope I helped!