Carry Over

Answer: M has the lowest value


Working out the possibilities
UK + 4 is three digits long so UK = 96, 97, 98 or 99
 
The only one with no repeats is 98 + 4 = 102
0 is the lowest, which is M.


Using algebra
$UK$ means $10U + K$ and $SMC$ means $100S + 10M + C$, so we have $$10U+K+4=100S+10M+C$$ The left hand side is at most $$10 \times 9 + 8 + 4 = 102$$ so $$100S+10M+C \leq 102$$ Therefore $S \leq 1$, so $S=1$ (since it can't be zero). So $$10M+C \leq2$$ So $M=0$

$M$ has the lowest value.