Amixture of potassium bromide and potassium hydroxide has a total mass of 5.50 g. if the mixture contains 2.45 g k, what is the mass in grams of potassium hydroxide in the mixture?

KBr molar mass = 39 + 80 = 119 grams which has x moles in the mixture
KOH molar mass = 39 + 17 = 56 grams which has y moles in the mixture

119x + 56 y = 5.50
39*x + 39*y = 2.45 that's because 

Every mole of KOH and KBr has exactly 1 mole of K in each molecule.

I won't go through the math, but the answer is
x = 0.0315
y = 0.0314
The answer to your question involves y*56 from which we get 1.758 grams Sodium Hydroxide

To check we
119x + 56y = 5.50 grams of mixture.
119* 0.0315 = 3.75 grams
56 * 0.0324 = 1.758
Total = 5.51 which is about as close as you can get when rounding.

It is a mixture. simply put, a compound must be pure, that is, of only one chemical structure and composition. a mixture is made of different chemical substances (i.e. elements, molecules, compounds) that are not chemically bonded to each other, but instead physically grouped together, as in the case of gasoline (a homogeneous solution).