[tex] \left(\begin{array}{ccc}n\\k\end{array}\right) [/tex] is for a binomial to the nth power, to find the k+1 term so 4+1=5 look at row coresponding to 6th power (7th row from top) cound 5 from left to right get 15 15(a)^1(b)^5 is 5th term in binomial (a+b)^6