We have 26 - 18 = 8; 34 - 26 = 8; 42 - 34 = 8; (an arithmetic progression)
We use the formula an = a1 + (n-1)x8 (the explicit formula)
So, an = 18 + (n-1)x8 ;
Then, an = 8n + 10;
Finally, a52 = 8x52 + 10 = 426 (the 52nd term);
The question is asking to state if those following scale factors are consider as contraction or expansion, base on my research and further analysis, the possible answer are the following:
3/2 expansion
1/3 contraction
4 contraction
2/5 contraction
4/3 expansion
1/4 contraction
I hope you are satisfied with my answer and feel free to ask for more if you have question and further clarifications