How to get Algorithm complexty based on another 2 algorithms?
The total running time of $_3$ will be bounded by $()+()$ where $$ is the size of the input to $_1 $and $$ is the size of the output of $1$. Now time complexity is usually written in terms of the size of the input of the algorithm and nothing else, so if $=()$ then the running time of $_3$ will be $\mathcal{O}(p(x)+q(f(x)))$