Solution:
We need to find 15-7 using two subtraction equation.
First we split 15 and 7 as addition form.
Split 15 = 10 + 5
Because sum of 10 and 5 is 15
Split 7 = 5 + 2
Because sum of 5 and 2 is 7
Now we substitute into original expression.
(10 + 5) - (5 + 2)
Now we open the parentheses
10 + 5 - 5 - 2
We can see two positive number and two negative number.
Now we move one positive and one negative number together
10 - 5 + 5 - 2
Now we close in parentheses.
(10 - 5) + (5 - 2)
Two subtraction equation:
10-5 and 5-2