I am having low budget... I need graphic card for casual gaming without focusing much on fpsYour motherboard has 1 PCIe 3.0 X16 slot. As long as nothing else is there, you can install any PCIe (pretty much everything made in the last 10+ years) ... that's assuming your power supply can handle it.
Not to be rude, but why the R7 240? There are faster cards out there that probably sell for the same price (I say that not knowing the price and what is available to you).