What is the pH of the solution that results from mixing the following four solutions together?

(1) 150. mL of 0.250 M NaCl
(2) 300. mL of 0.200 M HCl
(3) 100. mL of 0.050 M HNO3
(4) 450. mL of 0.200 M NaOAc

any help is greatly appreciated!

I would determine the molarity of each component.

moles NaCl = M x L
moles HCl = M x L.
moles HNO3 = M x L.
moles NaOAc = M x L.
Then M = moles/L.
for NaCl that will be 0.0375/1 L = ??
Likewise for the others.
Finally, add the two H^+ from HCl and HNO3 to obtain total H^+.
Then H^+ + OAc^- ==> HOAc
You know H^+, you know OAc^-, that makes HOAc and leaves some Ac^- un-reacted. Then use Ka expression or the Henderson-Hasselbalch equation to solve for pH.