This is presumably about linear graphs of the form y=ax+b, where a is the slope or gradient and b is the y intercept. The point (0,0) tells us that when x=0, y=0, so putting these in the equation, it means that b=0. We also know the slope is 3/4 so a=3/4 and the graph is y=3x/4 or 4y=3x.