Question

If x +y= 3 passes through a point (a,0)then the value of a

Answer 1

The line passes through (a, 0)
i.e. x=a and y=0
From equation of given line
x + y = 3
a + 0= 3
a= 3

Answer 2

In this :
x=a and y=0
then, by putting the values in the equation

a+0=3
a =3-0
a=3

I hope this helps you