The scale factor is 7.5 because if you divide 30 by 4 and 45 by 6, it is 7.5.
So to find the actual measurement of Harper's bedroom, you multiply 1.2 by 7.5, that would be 9 feet wide, and 1.6 by 7.5, that would be 12 feet long.
9 feet wide, 12 feet long