The equation is found first by measuring the slope of the line.
Slope is denoted by rise over run (rise/run), or y/x.
This is found by taking (y2-y1)/(x2-x1)
in the points given, x is the first value and y is the second, so x1=13, x2=16, y1=19 and y2=13.
Therefore, rise over run (slope)=
(13-19)/(16-13) = (-6/3) = -2
Furthermore, the equation of a straight line is always in the form y=mx+b, where m is the slope and b is the y-intercept (or where x=0). You can find b by plugging in either of the two points you are given in the equation
13= -32 +b
So the equation of the line (in y=mx+b format) is y= (-2)x + 45
You can verify that this equation is correct by plugging in x or y from the other set of values into the equation:
y= -2x + 45
y= -2(13) +45
y= -26 + 45
Hope this helps!