From the first one

Six stamps on a letter cover and the sum is 85 öre. This letter was bound for U.S. via airmail in December 1948. After some research I can not confirm any 85 öre postal rates for airmail to North America in 1948. The nearest I got is 80 öre for the weight class 5 - 10 g which was the rate effective from 1 January 1947 to 30 November 1949. My guess is that the sender did not have the right denominations at hand for exactly 80 öre and had to over frank the letter. The letter cover is not marked "5 g" which also indicates the higher weight class 5 - 10 g.

International letter fee 30 öre + airmail 5 - 10 g fee 30 öre,
over franked with 5 öre.
1948, 1 April. 10 öre green Gustaf V, right profile. Qty: 82,600,000, 3-sided perforation,
. . .  from the 84th booklet.
1945, 14 February. 15 öre brown Gustaf V, right profile, version I. Qty: 18,400,000 (pairs), 3-sided perforation,
. . . from the 71 th booklet.

According to the back side of the letter cover the sender was Professor Nanna Svartz, Stockholm. Mrs. Svartz was a pioneer in Swedish academics and she actually became the first female Professor in Sweden in 1938 at 48 years of age. She was a Professor in general medicine with a specialization in intestinal and rheumatic diseases.

To me it looks like it is a private letter to Dr. Amandus Johnson at Pennsylvania University. However that was apparently not the right address, some one has changed the address to 1300 Locus Street with a pencil. The Historical Society of Pennsylvania is residing at that address which indicates that Dr. Johnson is not a medical doctor. He was not, Dr Johnson was an American historian, author and the founder of the American Swedish Historical Museum. He came with is parents to Minnesota in 1880 when he was three years old. He became a quite famous Swedish-American, at least in Sweden.