firstly in equation y= 2x+6 suppose the value of y as zero and find the value of x. again suppose the value of x as 0 and find the value of y. Do the same for other equation as well and you get two values of X and y.
Also find the slope of each equation by the formula :
slope= - coefficient of x / coefficient of y. and solve by plotting the points according to the slope.
Divide the volume of the tank (10,000 gallons) by the filling rate of 250 gallons/minute and you will Hours = hr x min x 3785 ml x 55 gal = 208175 = 115.6 hrs.