To answer this question you need to understand how to change the description into an equation. I will split the description into two parts like this
"if 16 be subtracted from it, 1/7 of the remainder" ----->(X-16) * 1/7
"will be equal to 1/9 of the number"-----> = 1/9*X
If you join them you will get:
(X-16) * (1/7)= (1/9)*X
x-16= (1/9)*x /(1/7)
x-16= 7/9x
x- 7/9x= 16
2/9x= 16
x= 16*9/2= 72