First, calculate the slope.


    The formula for the slope of a straight line passing through two given points    (,)    and    (,)    is
        m = .

    Substitute the given data   = 1,   = 3,   = 3,  = 7  into the basic formula

        m =  =  = 2.


Next, find an equation of the line having the slope 2 and passing through the given point  A = (1,3).


    An equation of a straight line in a coordinate plane which has the slope  m  and passes through the given point  P = (a,b)  is 

        y - b = m*(x-a).     

    Substitute here  m = 2,  a = 2,  b = 3,  and you will get

        y - 3 = 2*(x-1).

    It is the equation in the slope-point form.

    If you want to have it in the slope-intercept form, transform it in this way

        y = 2x - 2 + 3,   or

        y = 2x + 1.