If the points (1, m), (- 2, n) are all on the image of the function y = - x + 2, then the value of Mn is?

If the points (1, m), (- 2, n) are all on the image of the function y = - x + 2, then the value of Mn is?

The values of M and N can be obtained by substituting two points into each other
m=-1+2 n=2+2
So m = 1, n = 4, Mn = 4