Hey Guys! I'm missing the d3dx9_39.dll file.

Hey guys!! I have a serious problem. I love LOL, I'm a dedicated player, and I'm looking to be a part time streamer but League of Legends does not seem to be working for me. I got league on a new pc that I built and something seems to be wrong. This is the problem. I log in. All good. I get into the queue. Still fine... I pick a champ and then as soon as the game starts, (and where the loading screen is supposed to be, I get this. "System Error The Program can't start because d3dx9_39.dll is missing from your computer. Try reinstalling the program to fix this problem." What do I do to get league running??? My operating system is Windows 10 Pro Please help me!!