Thanks for linking the case. The math here is quite tricky, but the case is correct!
So, for Men's market we multiply the market size ($100m) times its growth in 2 years (1.25^2). This is correct as the market grows 25% per year.
We then multiply it by .1 *.95^2 because "Market shares have been declining or stagnating in the last two years". Men's market share has been falling by 5% each year.
The teenager market is $50M (exhibit 1) and it's growing by 10% each year (Exhibit 1). Therefore we do $50M * 1.1^2.
The teenager market share is 25% (exhibit 2) and not declining (text above the math). Therefore we mutiply the above result with 25%, or 25% X 1 (no change).