The horizontal stretch is the correct answer. A period is the distance on the x-axis that it takes for the tangent or cotangent function to repeat itself. Stretching it out horizontally will lengthen that distance and therefore change the period.
He/she idk, got a higher score on the second test. How you do it is divide the score by the number out of it so like 19 divided by 25. Umm for the ratio, I'm not really sure, I guess you just do 19:25 and 17:20