Equation

how do you write this as an equation..
the sum of 100 and a number is equal to three times that number.

100+n=3(n)
sum of 100 and a number
n=number
equals 3 times that number
3(n)

100+x=3x

they are correct. the 3(n) and 3x in their example mean that they are multiplying.
Your job is to isolate the x to one side of the equal sign, and then you will know what the number was...

100+x = 3(x)

sum of = plus
if you see the word time = multiplying