How do I calculate consumer surplus and producer surplus from this?
In equilibrium, we have supply equal to demand. So $Q_{s} = Q_{d} \implies 50 = 2p$, so $p^{*} = 25$ is the equilibrium price. Consumer surplus is defined as:

$$\int_{p^{*}}^{p_{max}} Q_{d}(p) dp$$

Here, $p_{max} = 50$, as $Q_{s} = 0$ when $p = 50$. So evaluate the integral. 

Producer surplus is similarly defined as:

$$\int_{0}^{p^{*}} Q_{s}(p) dp$$