In order for two lines to be parallel, they need to have the same gradient (m). The gradient (m) is the coefficient of x in the line equation y=mx+c. Therefore, the gradient of L1 is 3 since 3 is the coefficient of x. For L2, you'll need to rearrange the equation so that you get it in the form of y=mx+c. So the first step would be to move -9x+5 to the right hand side: 3y=9x-5. Next, you'll have to divide everything by the coefficient of y (3). Therefore, you'll get y=3x-5/3. Now the gradient of L2 is 3 because x's coefficient is 3 and this is the same for L1 so the lines are parallel.