Question 143562
You sort of have the right idea, but your equation in part b should have been {{{y=3x}}}.  You got the correct solution to part c, but you didn't explain the steps to solving by substitution -- namely take the expression in x that is equal to y from the part b equation and substitute into the first equation, then solve for x.  After solving for x, use either equation to solve for y.


To determine the intercepts, and I'm supposing that you are talking about the y-intercepts, solve each equation for y.  {{{x+y=56}}} so {{{y=-x+56}}}.  Now the equation is in slope-intercept ({{{y=mx+b}}}) form where m is the slope (-1 in this case), and b is the y-coordinate of the y-intercept (56 in this case - meaning that the line intersects the y-axis at (0,56)).  Your second equation is already in slope-intercept form,  {{{y=3x}}} is the same as {{{y=3x+0}}}, so the slope is 3 and the intercept is 0 (the intercept is at the origin).  The point of intersection you will get by graphing the system is defined by the ordered pair created from the x and y values you calculated in part c of the problem, namely (14,42)


If my supposition was incorrect and you actually need both the x- and y-intercepts, then solve each equation for x.  The constant term that results will be the x-intercept.