The question says ..

match the equivalent addition and subtraction expressions
a) -6 -9
b)-10 - (-12)
c)6-9
d)10-12
e)-12-10

A)10+(-12)
B)-6+(-9)
C)-12 + (-10)
D)6+(-9)
E)-10+12

Convert a) through e) to addition expressions

Change the sign to + and change the sign of the number to the opposite of what it is.

a) -6 - 9 = -6 + (-9)
b) -10 - (-12) = -10 + 12

Now you do c), d) and e)