How do you write this equation?? steps please!!

If we add x ml of 100% acid to 100ml of 35% acid solution, the concentration C(x) of this new mixture can be expressed as...

a) x/x+100
b) x+0.35/100
c) x+35/x+100
d) 35/x+100

You have 100 ml of 35% acid, so the amount of
acid is .35 * 100 = 35ml.
If you add pure acid you are adding x ml of acid.
The total amount of solution as you add x is 100 + x.
So you have 35 + x acid in total solution of 100 + x.
Concentration is (35 + x)/(100 + x)

Idk