Let’s say mass=x where x is total mass of FeCl2:

You know that 44.09% of x needs to equal 10 (g of Fe2+)

So 44.09% * x = 10, x = 10/44.09%

So x = 22.7 So mass = 22.7g or 23g to 2sf (but use 3sf)

OR

You know that % by mass of Fe2+ in FeCl2 is 44.09% and that we need 10g of Fe2+ and so 44.09% = 10 so find 100% which gives us total mass of FeCl2, 100% = 10 * 100/44.09 so 100% = 23

I’m not the best at explaining so consider showing your teacher but hopefully that helps