Answer:
44
Step-by-step explanation:
(7^-1 - 8^-1)^-1 - (3^-1 - 4^-1)^-1
( 1/7 - 1/8 )^-1 -( 1/3 - 1/4)^-1
( 1/56)^-1 -( 1/12)^-1
56 -12
