Let us suppose missing term is y
so it becomes - ( x-1) + 5 = 2 ( x+3) - y
let us now try solving it for x ( in terms of y )
-x + 1 + 5 = = 2x + 6 - y
-x + 6 = 2x + 6 -y
6 + y = 2x + 6 +x
y = 3x
y / 3 = x
but x is given to be infinite . let us try placing y= the given options
x= x/3 which is not possible
x= 3x/3 which is giving valid statement
x= 1/3 which is a finite value
x= 5/3 again a finite value
so it is only y= 3x which could be the answer
Answer : option second that is 3x
