(4446)base x + (2222)base x=(10001)base x
now if you see closely when we adding 6+2=8 which is greater than 7 we are getting 1(8-7) and 1 will we the carry and after doing that we will get same output as 10001 at base 7
now to solve (2342)base 7 - (1656) base 7=(353)base 7