Answer: 
the answer is d.
Step-by-step explanation:
first, you want to use the formula, 
new value - original value 
<u>____________________</u>
          original value              * 100
you see that 84 is the new value and 79 would be the original value. substitute the numbers in. this is a increase since you will get a positive value.
84 - 79
<u>______</u>
    79      * 100
now we solve it. 
5
<u>__</u>
79  * 100
you can either solve the fraction first then multiply that by 100 or multiply the numerator by 100 first then divide that by 79, each way works.
500
<u>____</u>
  79   =  approximately 6.3% increase (this is not a exact value, just rounded)
       or 
5
<u>__</u>
79  = approximately 0.063 (this is not a exact value, just rounded)
0.063 * 100 = 6.3% increase