Question

How did president Roosevelt assist Britain while maintaining U.S. neutrality?

Answer 1

while initially keep in america out of world war 2 he provided financial assistance and equipment to Britain and its allies.

Answer 2

He introduced the Lend-Lease act

This was an act according to which he could provide help in the form of goods such as rations or munition or weapons or similar things to the allies who participated in the war, without actually actively being involved with American troops. Following the attack on Pearl Harbor, the US entered the war formally and wasn't neutral any longer.