Coefficient of t 24 in the expansion of 1+t2121+t121+t24 is
12C6+2
12C6+1
12C6
12C6+3
Coefficient of t 24 in 1+t2121+t121+t24
= Coefficient of t 24 in 1+12C1t2+12C2t4+…1+t12+t24
=12C12+12C6+1=12C6+2