Express 550 and 1645 in the scale of 2, 5, 6, and 9.

Answer 1

2+5+6+9 = 22
550/22 = 25, so multiply all the values by 25.

1645 done that way will give fractional values.

Answer 2

Ahh I see you meant base, not scale.
550 = 1000100110₂
550 = 671₉

what do you get for the others?