Question 1189392
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I will provide a response that solves the problem a bit more informally than the other tutor....<br>
Each of terms 5-8 is equal to the corresponding term among the first four terms, plus 4 times the common difference.  (The 5th term is 4 terms after the 1st, so it is equal to the first term plus 4 times the common difference; likewise for the other pairs of corresponding terms.)<br>
So the difference between the sum of the first four terms and the second four terms is 4*4=16 times the common difference.<br>
The difference between those sums is 48, so the common difference in the sequence is 48/16=3.<br>
Using a for the first term, and using the common difference of 3, the first four terms are<br>
a, a+3, a+6, a+9<br>
The sum of those first four terms is 26:<br>
(a)+(a+3)+(a+6)+(a+9) = 26
4a+18=26
4a=8
a=2<br>
ANSWERS: The first term is 2; the common difference is 3<br>