Dear Professor/Professors I'm sorry to trouble, with this thing tha might be so easy, I thought I knew but somehow I confused myself

For instance, I have a 100 ml solution of CuO and DI water where my CuO is 0.1 wt% .

my total solution should be 100 ml and to that suspension I want to add a small percentage of surfactant lets say the ratio 1:0.5 in relation with the CuO

So to get the g from wt% of CuO I used the followed wt% formula

[weight percentage of CuO I want] = X (g of solute, this case CuO) / 100 (of total solution) *100

I derivate by X and got as result 0.1 g of CuO

for the surfactant I'm not really sure, lets say I want the ratio [1:0.5] respect to the CuO ,

I already know that I need 0.1 g of cooper so that I multiply for

0.1 * (0.5/100) and then I get how much grams of surfactant I should add to my solution

then for the total DI water ill just substract g of CuO and surfactant from 380

this is how i think it is please enlight me if i am wrong but the other doubt that i have is that i dont know how will it be, if I use lets say 360, 420 ml ? should i divide the ratio i want in that example 0.5 by 360?

thank you for your time to read until here, looking forward for an answer