Answer :

3/8 is the answer

*Hope I Helped*
AL2006

In order to reduce ANY fraction to lowest terms, find any common factors
of the numerator and denominator, and divide them both by it.  If they still
have a common factor, then divide them by it again.  Eventually, they won't
have any common factor except ' 1 ', and then you'll know that the fraction is
in lowest terms.

Do  15  and  40  have any common factors ?
Let's see . . .

The factors of  15  are  1,  3,  5, and  15 .
The factors of  40  are  1,  2,  4,  5,  8,  10,  20, and  40 .

Ah hah !  Do you see that ' 5 ' on both lists ?  That's a common factor.

So  15/40  is NOT in lowest terms.

Divide the numerator and denominator both by  5 :

       15 / 40  =  3 / 8

3  and  8  don't have any common factor except ' 1 '. 
So  3/8  is the same number as  15/40, but in lowest terms.