I want to find the tangent space of $M$ in $p$, where M is defined by $z=x^2+y^2$ and $z=4-y$ and $p=(2,-1,5)$.
I know how to find tangent spaces of manifolds which are defined using one equation - I find function f and value a such that M = $f^{-1}(a)$ and than the tangent space equals $\text{ker}(df_p)$. here I don't find such $f$, and don't know how to continue.
Hint
Your manifold is defined as the intersection of two sub manifolds.
The tangent space (a line here) is the intersection of the tangent spaces (planes here) at $p$.