I dont understand this word problem

Question

Two bowls and one cup have a mass of 800 gram. One bowl and two cups have a mass of 700 grams. Find the mass of a bowl and the mass of a cup. Let the mass of a bowl be b grams and the mass of a cup be c grams.

Answer 1

1. Set up the equations
1. 2b + 1c = 800   {Eqn 1}
2. 1b + 2c = 700   {Eqn 2}
2. You have two unknowns (b and c) and two equations, so you can get a unique answer to the problem.
3. There are a couple of ways to do this.  I'll use the method of substitution:
1. In Eqn 1, solve for c.    So, c = 800 - 2b {Eqn 3}
2. Now substitute this value of c into Eqn 2.   So, 1b + 2* (800-2b) = 700
3. Solve for b. 
1. b +1600 -4b =700.  
2. -3b = -900  -->  b = 300
4. To find c, substitute this value of b back into eqn 3.   c= 800- 2(300) -->  c = 200
4. Check the answer, b = 300 and c = 200 by substituting these values into eqn 2.  Does 1b + 2c = 700?
1. 1(300) + 2(200) = 700?
2. 300 + 400 = 700
3. The check works.