-2x

3x+1

10

this is what i understood from what you typed...
The <em><u>correct answer</u></em> is:
They had no placeholding zero.
Explanation:
Our numbering system is one of few known to have a numeral for zero. Mayans did; however, theirs never traveled the world. Babylonians were thought to have a mark for nothing, but it was more for punctuation than numerals. Neither the Romans nor the Egyptians had a number for 0 either.
Zero is key to our system of numbering, as it helps us hold place as well as representing nothing. Without it, it is easier to represent problems in words.
15 because 150 divided by 15 is 10 and 135 divided by 9 is 15 and im 99% sure that's right because I couldn't think of anything higher
Lets use the distributive property to re-write this:-
18 + 36
2(9 + 18)
To make sure of this, lets solve
2*9 = 18
2*18 = 36
36 + 18 = 54
54 = 54 PERFECT
Answer: 2(9 + 18)