The sum of the first four terms of a linear sequence is 26,that of the next four terms is 74, find the values of the first term and the common difference

Answer 1

just use the formulas you know.
4/2 (2a+3d) = 26
Now, the next four terms' sum is the sum of the first 8 terms, minus the sum above
8/2 (2a+7d) - 26 = 74
Now just solve for a and d

Answer 2

a + a+d + a+2d + a+ 3d = 26
a+4d + a+5d + a+6d + a+7d = 74
well
4 a + 6 d = 26
4 a + 22 d = 74
---------------------
0 - 16 d = - 48
d = 3
etc