a)$ |h(x)| \leq (\int |f(x-y)|^p dy)^{1/p}(\int |g(y)|^q dy)^{1/q} = (\int |f(z)|^p dz)^{1/p}(\int |g(y)|^q dy)^{1/q} \leq ||f||_{p}||g||_{q} $
b)Define $ f_{t}(x)=f(x+t)\frac{}{} $, $ h_{t}(x)=h(x+t)\frac{}{} $.
We have
$ |h_{t}(x) - h(x)| = |\int[f_t(x-y)-f(x-y)]g(y)dy| \leq \int|f_t(x-y)-f(x-y)| |g(y)| dy \leq ||f_t-f||_{p}||g||_{q} $
