AB and WX because the length is directly the same
Check if you can write an equation relating the term number to the actual value
n1=3
n2=10 = 3+7
n3= 17 = n2+7 = n1+7+7 = n1 +2*7
n4= 24 = n1+3*7
so you will notice a pattern
for the x-th term
n_x =3+(x-1)*7
the 50th term would be n_50 = 3+(50-1) * 7
First term [ a ] = 6.3
Common difference [ d ] = 8.8 - 6.3 = 2.5
Using general term formula,

78.8 = 6.3 + (n-1)*2.5
2.5*(n-1) = 72.5 [ Dividing both sides by 2.5 ]
n-1 = 29
n = 30
Hence, 78.8 is the
30th term in the arithmetic series.