Before 4 years, dog A’s age was 4 times of dog B’s age and after 4 years, dog A’s age will be 3 times of dog B’s age. What is the difference of dog A’s age and dog B’s now?	Choose one.
A) 36
B) 42
C) 52
D) 60
E) 64
A - 4 = 4(B - 4) --&gt; A - 4B = -12.............1   A + 4 = 3(B + 4) --&gt; A - 3B = 8.............2   (2) - (1) --&gt; B = 20 --&gt; A = 3(24) = 72   A - B = 72 - 20= 
<gadget id="calculator">72 - 20</gadget>
<output>52</output>
52   Answer: 52
<result>C</result>
Before 4 years, dog A’s age was 4 times of dog B’s age and after 4 years, dog A’s age will be 3 times of dog B’s age. What is the difference of dog A’s age and dog B’s now?