Çözüldü Percentage Problem

The number a is 70% less than the positive number b. The number c is 60% greater than a. The number c is how many times b?
https://satsuite.collegeboard.org/media/pdf/psat-8-9-practice-test-1.pdf [Module 1, Page 36 (38 in the pdf file), Question 27]
Answer key: https://satsuite.collegeboard.org/media/pdf/psat-8-9-practice-test-1-scoring-guide.pdf

Pure Algebraic Solution Without Needing To Use Any Numerical Substitution:
a = b·(1 - 70 / 100) = 3b / 10....(I)
c = a·(1 + 60 / 100) = 8a / 5....(II)
Multiplying the equations (I) and (II) side by side and simplifying; c = (12 / 25)·b or c = (48 / 100) = 0.48·b.