Answer: B) one solution 
Reason: if we solve for the sides of the equation by putting like terms together we get that x = 3 
There is no solution when the numbers don’t equal each other, take for instance 1 = 2 
It has infinite solutions when the numbers are equal to each other like 
1 = 1
It has one solution when the x value is equal to something like x = 9
I also worked out the equation on paper, so you could get a more visual way of how I solved it.
Hope this helps