the answer
the question is not clear
if it is to determine how to write this phrase as a mathematics equation, it is as follow:
let be x the unknown number
so ighty-seven decreased by three times a number is greater than one hundred sixty-five means 87 - 3x>165,
so we can solve it easily as 87 - 165> 3x, and then 3 x > 32, and finally the value of x is x > 32/3=10.66