My first step was to change the format to 1/(10+h) - 1/10 over h and i get -h/h which still wont work.... how should i go on from here?
Express the numerator over a common denominator. Then the thing you're taking the limit of can be written $\displaystyle \frac{10 - (10 + h)}{10h(10 + h)}$. Simplify and take the limit.