Option B.
$L1^{3}$ = L1 . L1 . L1 (Concatenation of L1 3 times).
You have already found the Grammar of L1.
Just add this line in your production of L1.
X $\rightarrow$ SSS
Now X will be the start symbol.
Option C.
L1* = $L1^{0}$ $\cup$ $L1^{1}$ $\cup$ $L1^{2}$ $\cup$ ....... So on.
Add this line in the production of L1.
Y $\rightarrow$ SY / $\epsilon$
Now Y will be Start symbol.