No, you can only use British stamps for mail posted in London. (You wouldn't expect to be able to use a stamp from a different country on a letter mailed in the USA.)
One.
1 oz letter to UK is .94
That is what the US issues stamps for, so that you can send mail to anyplace in the world.
Ask at a post office in USA !
yes- the rate is 98 cents for an ordinary letter of no more than one ounce.
A single First Class stamp is adequate for a one ounce regular letter.
how many forever stamps = .94
what the price to mail letter to
5
No, the postman will ignore it. Go get stamps.
No, you must use US postage stamps.