The graph of function b(x) can be seen in the image at the end.
How to graph the translation?
Here we start with the function f(x) = 10x. And we want to find the graph of:
b(x) = f(x) - 30
This is just a translation of 30 units down of the graph of f, remember that a vertical translation of N units is defined as:
g(x) = f(x) + N
So just take the graph of f and move it down 30 units, you will get the graph you can see below.