math questions

What is the unit digit of 18的42次方??
18^42
= (20 - 2)^42
= 20^42 + ... + (42)(20) (-2)^41 + (-2)^42
前 42 項 unit digit 係零,因為乘 20
unit digit of 18^42 = unit digit of (-2)^42
unit digit of 2^1 = 2
unit digit of 2^2 = 4
unit digit of 2^3 = 8
unit digit of 2^4 = 6
unit digit of 2^5 = 2
unit digit of 2^6 = 4
...
unit digit of 2^42 = 4
unit digit of 18^42 = 4
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For 0<1000,how vmany integers m will make m(2次方)+7over m-4 into a simplest fraction??
我想知 m^2 + 7/(m-4) 定係 m^2 + 7/m - 4 定係 (m^2 + 7)/(m-4)
差好遠架