Find three consecutive largest positive integers such that the sum of one-third of first, one-fourth of second and one-fifth of third is at most 20.

Find the greatest value of x ∈ Z, so that :

-1 ≤ 3 + 4x < 23

If 7 ≥ -2x + 1 > -7 ; find the sum of greatest and smallest values of x ∈ I.