3. sophie and jackie each have a collection of baseball cards, jackie has 5 more cards than
sophie, and together they have 30 cards. by writing and solving an equation, find out how
many cards sophie owns. show all of your working out.

Sophie has 12.5 cards

Step-by-step explanation:

Let

x > number of cards Sophie has

y > number of cards Jackie has

we know that

x+y=30 > equation A  

y=x+5 > equation B

Solve by substitution

Substitute equation B in equation A and solve for x

x+(x+5)=30

2x=30-5

x=12.5 cards

Note I assume the problem was invented without taking into account the result, because the amount of cards should be a whole number