Calle: has twice as many as Juniper so = 2*25 = 50
she also has 5 times as many as sara so if she has 50, you divide 50/5 = 10
Calle has 50 stickers, Sara has 10 and Juniper has 25.
So all together they have 85 stickers.

Actually Welcome to the Concept of the Similarities.
Since here, first figure is a Triangle, hence similarity of a triangle is given by ratio of it sides and make them equate,
hence for,
1.) 16/12 = x/9 ===> 4/3 = x/9 ===> x = 9*4/3 ==> x = 36/3
hence the value of x is 12 , ===> x = 12 .
2.) here,in the case of a Reactangle the relation is such that, length = 2* breadth,
hence we apply the relation,
x = 2*4.5 ===> x = 9 units.