chemistry
posted by katie on .
Calculate the volume of a 9.00 M HNO3 stock solution that must be used to prepare 450 mL 0f a 1.80 M HNO3 solution.

M x V = M x V (good for dilution problems only).

so which ones do i times together?

molarity of concd HNO3 x mL concd HNO3 = molarity of the diluted solution x mL of the diluted solution.

so is just 9.00x 450x1.80??

9.00 x 450x 1.80?

Where is the equal sign?
I would do it this way.
9.00 M x ??mL = 1.80 M x 450 mL
and solve for ?? mL.
Isn't that what my instructions said?
M concd soln x mL concn soln = M dilute soln x mL dilute soln. 
9.00x?mL=810
how do i find the missing number 
You solve for ? mL. This is an ordinary equation.
9.00 x unknown mL = 810.
Solve for unknown mL. 
ok so to find it...do i subtract them..or divide?

You divide. It has taken me most of the night but I think I know what your problem is. It isn't chemistry. It is arithmetic and algebra. You apparently don't know how to solve an equation.
When we had pH + pOH = 14 and we substituted to give
9.21 + pOH = 14, I had to tell you that pOH = 14  9.21 and you obtained the correct answer of 4.79.
For this problem, we have 9.00X = 810.
You solve for the unknown by
X = 810/9.00 = 90; therefore, you take 90 mL of the concd HNO3 (which is 9.00 M), make the total volume to 450 mL, and you end up with 450 mL of 1.80 M HNO3. I recommend that you find a tutor who can help you with algebraic manipulations.
You will do your self a huge favor if you contact someone at your school (a counselor, department head, etc) and ask about a tutor.