First: work out the difference (increase) between the two numbers you are comparing. Then: divide the increase by the original number and multiply the answer by 100. % increase = Increase ÷ Original Number × 100. If your answer is a negative number, then this is a percentage decrease. ( copy and paste from skillsyouneed.com )
The answer is b:
First change the operation to multiplication, and then change the last fraction to it's reciprocal (7/15 / 5/3)
Then, you can simplify 15 and 5 to 3 and 1 (divide each by 3)
Finally u multiply (7*1 / 3*3)
Sorry if its bad first time
K = 75
75-25=50
Hope this helps!