Deriving Transfer function from position block diagram
Just put some formula onto the various nodes: -



Can you see how this works and how E(s) becomes: -

$$R(s) - Y(s)$$

Therefore: - 

$$Y(s) = (R(s) - Y(s)) \cdot \left( \dfrac{K}{(s+3)(s+5)}\cdot\dfrac{1}{s}\right)$$

Just rearrange to group Y(s) terms and solve. Can you take it from here (it should be fairly straightforward)?