Marty earned $300 in interest on a deposit that was in an account for 8 years at
a rate of 3%. What was Marty's initial
deposit?

The reason why both graphs are parallel because they have the same slope but different y-intercept.

Think about it. If both graphs have same slope and same y-intercept. The graph will intercept each others infinitely.

Then if we change the y-intercept into any numbers that aren't the same as another equations for ex.

y = -5x+1 and y = -5x+10

then we will get the parallel graph. Or if you solve the equation, the equation will not be true, thus giving the graph parallel.

But if it is y = -5x+1 and y = -5x+1 which both are the same graph. Then the graph will intercept each others infinitely. Or if we solve the equation, we will get 0 = 0 which makes the equation true for all real numbers.

Therefore, the reason why both graphs are parallel is because that they have the same slope but different y-intercept.

That's all.