Base B (aka p) is equivalent to 18
p=18
Subtract the sale price from the original price then divide the difference by the original price.
Guitar 1: 160 -100 = 60
60/160 = 0.375 x 100 = 37.5%
Guitar 2: 250 - 150 = 100
100/250 = 0.4 x 100 = 40%
The answer is the second guitar has a greater percent change of approximately 40%
23:8 is the simplest form. However, you can put 5.75:2 or even 2.86/1 if you are looking for the absolute simplest