Let $W_k$ be the event of drawing a white marble on the $k$-th draw, and $B_k$ the complementary event.
So your solution should look somewhat like:
(a) $$\begin{align}\mathsf P(W_1\mid W_2)&=\dfrac{\mathsf P(W_1)~\mathsf P(W_2\mid W_1)}{\mathsf P(W_1)~\mathsf P(W_2\mid W_1)+\mathsf P(B_1)~\mathsf P(W_2\mid B_1)}\\[1ex]&=\dfrac{\tfrac{4}{4+9}\tfrac{3}{3+11}}{\tfrac{4}{4+9}\tfrac{3}{3+11}+\tfrac{9}{4+9}\tfrac{6}{6+8}}&=\dfrac{4(4-1)}{4(4-1)+9(4+2)}\\[1ex]&=\dfrac{2}{11}&\checkmark\end{align}$$
The others use Bayes' Rule too. Hint: tackle (c) first.
(b) $$\begin{align}\mathsf P(W_1\mid W_3)&=\dfrac{\mathsf P(W_1,W_2,W_3)+\mathsf P(W_1,B_2,W_3)}{\mathsf P(W_1,W_2,W_3)+\mathsf P(W_1,B_2,W_3)+\mathsf P(B_1,W_2,W_3)+\mathsf P(B_1,B_2,W_3)}\\[2ex]&=\tfrac{\mathsf P(W_1)~\big(\mathsf P(W_2\mid W_1)~\mathsf P(W_3\mid W_1,W_2)+\mathsf P(B_2\mid W_1)~\mathsf P(W_3\mid W_1,B_2)\big)}{{\mathsf P(W_1)~\big(\mathsf P(W_2\mid W_1)~\mathsf P(W_3\mid W_1,W_2)} + {\mathsf P(B_2\mid W_1)~\mathsf P(W_3\mid W_1,B_2)\big)+\mathsf P(B_1)~\big(\mathsf P(W_2\mid B_1)~\mathsf P(W_3\mid B_1,W_2)+\mathsf P(B_2\mid B_1)~\mathsf P(W_3\mid B_1,B_2)\big)}}\end{align}$$
(c) $$\begin{align}\mathsf P(W_1\mid W_2,W_3)&=\dfrac{\mathsf P(W_1)~\mathsf P(W_2\mid W_1)~\mathsf P(W_3\mid W_1,W_2)}{\mathsf P(W_1)~\mathsf P(W_2\mid W_1)~\mathsf P(W_3\mid W_1,W_2)+\mathsf P(B_1)~\mathsf P(W_2\mid B_1)~\mathsf P(W_3\mid B_1,W_2)}\end{align}$$
Best Answer
Suppose there are $n$ red marbles and $n$ black ones. We choose a marble from the urn. There are $n-1$ matching marbles left among the $2n-1$ marbles in the urn, so the probability that the first two match is $${n-1\over2n-1}<\frac12$$
Now suppose the first two match. We may assume that there are $n-2$ black marbles and $n$ red marbles left. There are ${n-2\choose2}$ ways to choose two matching black marbles, ${n\choose2}$ ways to choose two matching red marbles, and ${2n-2\choose2}$ ways to choose two marbles. Can you finish it from here?