Jacob has six times as many baseball cards as his sister rebecca. together they have a total of 861 cards. write an equation and solve to find how many cards they each have.

Let Rebecca equal x and Jacob equal 6x.  
6x + x = 861
7x = 861
Multiply both sides by the reciprocal of 7 which is 1/7.
(1/7)7x = 861(1/7)
x = 123
Since Rebecca equals x we know that she has 123 cards.  If we multiply this answer by 6 we get the number of cards Jacob has.
6(123) = 738
Therefore the final answer is:
Jacob = 738
Rebecca = 123
I hope this helps:)
Please comment if there are any problems.