First, find the common denominator of 12 and 15. The easiest one would be 60. Now since you multiply 12x5 to get 60, multiply 7 (numerator) by 5 to get 35. Do the same to other fraction exceptt mulitplying numerator by 4 since 15x4=60. You should now have 35/60 divided by 56/60. Change the division sign to mulptiplication sign. Now find the reciprocal of 56/60 which is 60/56. Now just simply mulitply across and you should get 2100/3360. Now just simplify or put in lowest terms. Divide both numerator and denominator by 5. You should then get 420/672. Now divide both by 2. You should get 210/336. Now divide both by 3. You should get 70/112. Now again divide both by 2. Finally, divide both by 7 and the final answer should be 5/8.