Here the unknown number is n . Product of 6 and n is 6n. And 6n is increased by 13 that is 6n +13. And the result is -14 , that is
6n+13=-14
We need to get rid of 13, so we subtract 13 to both sides, that is
6n = -14-13
6n =-27
Now we need to get rid of 6,and for that we divide both sides by 6, that is
n = -27/6
And that's the required value of n .