These are both straight lines.
In the first one it is easy to get the x intercept by subtracting 7 successively from the ordinate and 4 from the abscissa to find (0,-2) as a point on the line. Since this is a linear function, the y-intercept is 1/2 way between 0 and -7, i.e. -7/2.
However, in general you should probably find the equation of the line joining the points and get the intercepts from the equation.
In the 2nd set the slope is (1 - 3)/[0-(-3)] = -2/3. Use this to find the equation and then get the intercepts.
If you are still stuck, send me a message.
