Answer
10; $20\pi$
Work Step by Step
We know that if $A$ is a real number and $B\gt0$, then the graphs of $y=Asin(Bx)$ and $y=Acos(Bx)$ will have an amplitude of $|A|$ and a period of $\frac{2\pi}{B}$.
Therefore, the amplitude of the graph of $y=-10cos\frac{x}{10}$ is $|-10|=10$
Therefore, the period of the graph of $y=-10cos\frac{x}{10}$ is $\frac{2\pi}{\frac{1}{10}}=2\pi\times10=20\pi$.