We need to find the number of textbooks of each type that were sold.
Let's call C the number of Chemistry books and P the number of Physics books that were sold.
Since the store sold a combined total of 252, we have:
Also, the number of chemistry textbooks sold was 78 more than the number of physics textbooks sold:
Then, in order to find the value of P, we can replace C with 78+P in the first equation. We obtain:
Now, we can use the above result to find C:
Therefore, the answers are:
• Number of chemistry textbooks sold:, ,165
• Number of physics textbooks sold:, ,87