Let:
x = Chemistry textbooks sold
y = Physics textbooks sold
The textbook store sold a combined total of 260, so:

The number of chemistry books sold was three times the number of physics textbooks sold, so:

Let:

Replace (2) into (1):

Replace the value of y into (2):
Answer:
see explanation
Step-by-step explanation:
The meaning of n factorial → n !
n ! = n(n - 1)(n - 2)........ × 3 × 2 × 1
For example
7 !
= 7 × 6 × 5 × 4 × 3 × 2 × 1
A. define the variables : a = abby's miles, j = james' miles
b. a = j + 4......j = a - 4
c. a + j = 28
a = j + 4
d. (j + 4) + j = 28
2j + 4 = 28
2j = 28 - 4
2j = 24
j = 24/2
j = 12
a = j + 4
a = 12 + 4
a = 16
e. check..
a + j = 28
16 + 12 = 28
28 = 28 (correct)
solution is : abby's miles (a) = 16
james' miles (j) = 12
Associative property of addition