Question

Plzzzz plz help plz I don’t get it

Answer 1

$\bf \begin{cases} r=\textit{Richard's bookmarks amount}\\ R=\textit{Rose's bookmarks amount}\\[-0.5em] \hrulefill\\ \stackrel{\textit{but we know their amount is the same}}{r=R} \end{cases}~\hspace{5em} \begin{array}{llll} \stackrel{\textit{Richard gave away 28}}{r-28}\\\\ \stackrel{\textit{Rose threw away 16}}{R-16} \end{array} \\\\[-0.35em] \rule{34em}{0.25pt}$

$\bf \stackrel{\textit{after they got rid of those, the ratio r:R is 2:5}}{\cfrac{\textit{Richard new amount}}{\textit{Rose new amount}}\qquad \cfrac{r-28}{R-16}=\cfrac{2}{5}}~\hspace{5em}\stackrel{\textit{since we know r=R}}{\cfrac{r-28}{r-16}=\cfrac{2}{5}} \\\\[-0.35em] ~\dotfill\\\\ 5(r-28)=2(r-16)\implies 5r-140=2r-32\implies 3r=108 \\\\\\ r=\cfrac{108}{3}\implies \blacktriangleright r=36=R \blacktriangleleft$