If d is the common difference, q=p+d, r=p+2d, s=p+3d, t=p+4d.
So p+q+r=p+p+d+p+2d=3p+3d=9, p+d=3, and p=3-d.
s+t=p+3d+p+4d=2p+7d=26.
Substitute p=3-d:
2(3-d)+7d=26,
6-2d+7d=26,
5d=20, so d=4 and p=3-d=-1.
So the first term is -1 and the common difference is 4:
-1, 3, 7, 11, 15