You can calculate that expression and see if its divisble by 7.

So 5^2 * 31 * 43 * 10^6=33325000000 and divide that by 7 to see if integer comes up.

But another simpler way to see that 7 isn't factor is by looking at all factors at expression. So from expression we have factors 5,31,43 and 10 so 7 isn't factor.