Here's my step-by-step explanation:
Let's get two facts straight: f(x) is a linear function. It's a line. g(x) is an exponential function. It's a curve.
Method 1: Elimination using f(x)
For f(x), the y-intercept (where on the y-axis it coincides with) in {f(x) = 7/3x - 3} is -3. And the only graph that has that is Graph 2.
Alright, so the first obvious solution, according to that graph, is (0, -3). And since we're speaking in terms of x (thus f(x) and g(x)), we pick the x-value from that coordinate and get 0.
The second solution is not as obvious; it's supposed to be (3,4) but the graph is kinda off. I attached a Desmos graph so you can see what I'm talking about a little more clearly.
Anyway, since we're speaking in terms of x we pick the x-value from that coordinate and get 3. Nice, we've got the solutions 0 and 3.
Hope this helps, let me know if I made a mistake.