That's a normal speed for usb 2.0 and since it's transfer from/to it, that will be the limiting factor. If it's from your hdd to the usb 3.0 device then you would be running at usb 3.0 speed, assuming you also have it plugged into a usb 3.0 port.
I have 2 portable hard drive, USB 2.0 and USB 3.0.
1.) Transfer a file from USB 2.0 to USB 3.0 hdd stuck at 24MB/s and vice versa is that a normal ? or any other way to speed it up ?
no, sorry i just had that question the other day and after 30 years in IT I really should have know before i asked. the fastest you'll achieve is the speed of your slowest connection. In this case it's the 2.0 connection. only when we start seeing devices coming out (like our laptops/tablets) with 3.0 interface we won't actually (theoretically) see the touted 4.8/5.0 Gbps speeds.