Use workspace variable in equation solver

I have the equation x+y=25 and currently I have y as a predfined variable=5. so the equation becomes x+5=25. However I would like to change y from my script and the equation to automatically change based on my y value rather than me modifying my equations each time to edit the y value.

I currently do it this way:

y=5;

syms x
eqn = x+5=25;
S = solve(eqn,x);

Answer 1

[Rik]

If you don't want to use a function to wrap the input, you can use an anonymous function instead.

y=5;

syms x
eqn =@(y) x+y==25;
S = solve(eqn(y),x)

S = 

20

Answer 2

[Walter Roberson]

syms x y
eqn = x + y == 25

eqn = 

y = 5

y = 5

subs(eqn)

ans = 

y = 9

y = 9

subs(eqn)

ans =