Question 800737
first pattern is 3, 6, 9, 12, 15,18 and
the nth term is 3+(n-1)3
second pattern is 1, 3, 6, 10 and 
the nth term is n(n+1)/2
we now add the two formulas
3+(n-1)3 + n(n+1)/2 = 3n + (n^2+n) /2 = (n^2 +7n) / 2