We don’t know how many terms in the whole sequence but if all three sequences start and end at the same point, there must be both an odd number of terms and one more than a multiple of three terms. So there must be 6m+1 terms.

S is the sum of all 6m+1 terms.

88 is the sum of 3m+1 terms.

60 is the sum of 2m+1 terms.

All three sequences will have the same average since they are arithmetic sequences beginning and ending on the same terms, therefore:

S/(6m+1)=88/(3m+1)=60/(2m+1)

Taking just the last two terms and cross-multiplying:

88(2m+1)=60(3m+1)

176m+88=180m+60

4m=28

m=7

There are therefore 6*7+1=43 terms in the whole sequence.

Now just taking the first two terms and using the newly discovered value for m:

S*22=88*43

S=172

In all three sequences the average of the sequence will be 4. Therefore the middle (22nd)term of the full sequence will be 4.

If the first term is 0, and it needs 21 steps to get from there to the 22nd term, the common difference will be 4/21.