A bag contains blue marbles and red marbles, 107 in total. The number of blue marbles is 7 more than 4 times the number of red marbles. How many blue marbles are there?
Let the number of red marbles = R
Then the number of blue marbles = 4R + 7
So
R + ( 4R + 7) = 107 simplify
5R + 7 = 107 subtract 7 from both sides
5R = 100 divide both sides by 5
R = 20 = red marbles
4 (20) + 7 = 87 = blue marbles
