Why did congress need to form a "real" army

Why is it useful for historians to base certain studies on the analysis of historical periods

Germany italy and japan formed the tripartite pact in part because they: a. add chicken wings to the united states to stay out of world war ii b. share the ruling philosophies based on communist economics c. resented the agreements they were forced to sign at the munich conference d. selena territories were threatened by aggressive foreign states

If f(x) = 3x + 2 and g(x) = 2x - 2. what is (f - g)(x)?