Bigger then or greater then

Greater than. Both would be understood.

In that sentence "greater" would be preferable. Although it is also used figuratively, "big" generally refers to the physical size of something. "Larger" is similar, but it more often used to refer to things that are not physical objects. It is often used to just mean "more than," like "greater" is.

By the way: In your thread title, the word you're looking for is "than," not "then." Roger told you that, but in a subtle way that might not be obvious to you.

http://www.onemathematicalcat.org/algebra_book/online_problems/big_small.htm

10a + b = 9 * (a + b)

a = 8b

81

Correct

That's a great site. Thanks