Store A have a 30% off the original price. Convert percent into a decimal.
30% becomes .30. Now for Store B. It said $250 less. So, it would mean p - 250. Now back to the 30% part. We converted it into a decimal. Now, take that 0.30 and subtract from 1.00. The reason we do this is because 30% off the original price. 1.00 - .30 = 0.7. Or you could have done this earlier when it was still a percent. 100% - 30% = 70%.
Now the final equation we get is 0.7p = p - 250