Answer: 70-20x = 60-15x, where x is the number of pizzas purchased.
Explanation:
(TLDR, the solution to the given equation is that the cards will have the same amount of money left on them if both jim and clara buy two pizzas each. feel free read my explanation on how to write equations like this in the future, should you need it.)
so, we know that since jim and clara received $70 and $60 gift cards (respectively), these numbers are called constants, because their original values do not depend on anything (they are given). while these numbers may decrease with the amount of pizzas bought, their original values are fixed.
now, the price for one pizza at jim's pizza restaurant is $20, right? so if you buy 2 pizzas, it'll be $40, 3 pizzas are $60, and so on. but we can actually represent the price of the pizzas as 20x (where x is the number of purchased pizzas, and 20 is the price of one pizza), and this expression works for any number of pizzas you buy. you can also apply this to clara's restaurant, as the total price of the number of pizzas she buys is represented by 15x.
the words charges and left in this problem tells you that you're going to need to subtract from the total amount of money on the gift cards. using the expressions above, the amount of money jim has left on his card can be expressed as 70 (amount of money on the card) MINUS 20x (number of money spent on however many pizzas were bought (x)). likewise, the amount of money left on clara's card after she buys however many pizzas can be represented as 60-15x. you can then set the equations equal to each other and solve for x, which tells you how many pizzas they each need to buy to have the same number of $$ left on their cards.
70-20x = 60-15x
10=5x
2=x. hope this helped :3