Edexcel M3 Elastic strings and springs

Question
https://gyazo.com/fdbf4f5ccd10347a17a4610adada3f30
Textbook's solution
https://gyazo.com/7bb2a45cf3a9cc640ff6fd826a9c5fd3

My question: When they worked out the increased tension in Qb, shouldn't they minus the original tension which is found in the question(175N)? but instead they minus it by the modulus of elasticity of the string? Is there a mistake in the textbook?
Thanks in advance.

Yep, error in book. Should be 245-175.