Can some one explain to me what substitution is and how to use it to solve equations?

M the table below represents a linear function f(x) and the equation represents a function g(x): x f(x)−1 −50 −11 3g(x)g(x) = 2x − 7part a: write a sentence to compare the slope of the two functions and show the steps you used to determine the slope of f(x) and g(x). (6 points)part b: which function has a greater y-intercept? justify your answer. (4 points)