Cody was 165\,\text{cm}165cm165, space, c, m tall on the first day of school this year, which was 10\%10%10, percent taller than he was on the first day of school last year. how tall was cody on the first day of school last year?

Assume that Cody was x cm tall on his first day at school last year.
Assume that Cody is y cm tall on his first day at school this year.
This year, Cody became 10% taller.
10% is equivalent to 0.1

This can be translated into the following:
y = x + 0.1x 
We are given that y = 165 cm.
Substitute in the equation to get x as follows:
165 = x + 0.1x
165 = 1.1x
x = 150 cm

Based on the above calculations, Cody was 150 cm tall on his first day at school last year.