Kata

If you don't know what pascal's triangle is,go to https://en.wikipedia.org/wiki/Pascal's_triangle to learn about it.
pascal's triangle can be represented on a graph like so:
^ 1 4 10 20
| 1 3 6 10
| 1 2 3 4
y 1 1 1 1
x --------->

which still follows the rule.Your job is to find the value of any value on this graph,given its coordinates
Ex:
solution(4,5):
^ 1 5 15 35
| 1 4 10 20
| 1 3 6 10
| 1 2 3 4
y 1 1 1 1
x --------->
The answer is 35 because the space 4 spaces right and 5 spaces up of the origin is 35 on the graph.
Expect x and y to be positive integers and their sum to be less than 30