If you would like to know how many people attended the reunion last year, you can calculate this using the following steps:
125% of last year's attendance is 160 people
125% of x is 160
125% * x = 160
125/100 * x = 160 /*100/125
x = 160 * 100 / 125
x = 128 people (last year)
Result: 128 people attended the reunion last year.