For the first part it would be a good idea to sketch out the graph. Then using the formula 'change in y/change in x' find the gradient of the line (-4/3). You can then either use the formula y=mx+c and put in one of the points and gradient to find c or use the formula y-y1=m(x-x1) with one of the points. The equation of the line is =-(4/3)x + (47/3)
For the second part it again might be helpful to add to the sketch. Use simultaneous equations set the equations equal to one another and solve for x=58/17