a,b are two +ve no.s : a<4,b<4. Find the probability that 2a+3b<14? the ans is given as 13/16. can u tell me how is it so?

'a' can take values 1, 2, 3. 'b' can take values 1, 2, 3.
If a = 1 and b goes from 1 to 3, 2a + 3b takes values 5, 8, 11
If a = 2 and b goes from 1 to 3, 2a + 3b takes values 7, 10, 13
If a = 3 and b goes from 1 to 3, 2a + 3b takes values 9, 12, 15

So, probability that 2a + 3b < 14 is 8/9