4+1, 3+2, 2+3, 1+4. 4 total combinations, unless 4+1 and 1+4 are the same. In that case, there are only 2, 1+4, and 2+3
A mixed fraction... is made out of a whole number and a fraction. 3 7/10
I suppose you're supposed to convert 100111 from base 2 to base 10. We have

so the missing number is 39.
X^2 + X - 12 = 0
(X + 4)(X - 3) = 0
X = -4 and X = 3.