To convey as an algebraic expression simply break down the statements and use any variable to represent the number in the sentence.
10 • x^2 = 40x
10x^2 = 40x
10x^2 - 40x = 0
10(x^2 - 4x) = 0
X(x - 4) = 0
X = 0
X - 4 = 0
X = 4.
Here are two possibilities of what the number can be, but because it is a nonzero number, I believe it would be 4.
