Let the point is (1, 2)

and equation of the straight line is x + y - 1 = 0 

=> x + y = 1 ............1

=> y = -x + 1

Slope of the given line m₁ = -1

Slope of the line perpendiculat to this line m₂ = -1/m₁ = -1/-1 = 1

Now, Equation of staraight line having slope 1 and passing through the point (1, 2) is

      y - 2 = 1(x - 1)

=> y - 2 = x - 1

=> x - 1 - y = -2

=> x - y = -2 + 1

=> x - y = -1 ..........2

After solving equation 1 and 2, we get

x = 0, y = 1

So, the coordinate of foot of perpendicular is (0, 1)