Let:
C1 = Possible combinations for 11th grade
C2 = Possible combintations for 12th grade
TC = Total different groupings
For C1:
[tex]\begin{gathered} C1(n1,k1)=\frac{n1!}{k1!(n1-k1)!} \\ where\colon \\ n1=14 \\ k1=2 \\ so\colon \\ C1=91 \end{gathered}[/tex]For C2:
[tex]\begin{gathered} C2(n2,k2)=\frac{n2!}{k2!(n2-k2)!} \\ where\colon \\ n2=16 \\ k2=3 \\ so\colon \\ C2=560 \end{gathered}[/tex]Therefore:
[tex]\begin{gathered} TC=C1+C2 \\ TC=560+91 \\ TC=651 \end{gathered}[/tex]