Before 7 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 the most appropriate option.
A) 36
B) 42
C) 54
D) 60
E) 70
A - 7 = 4(B - 7) --&gt; A - 4B = -21.............1   A + 4 = 3(B + 4) --&gt; A - 3B = 8.............2   (2) - (1) --&gt; B = 29 --&gt; A =3(22)=99   A - B = 99 - 29= 
<gadget id="calculator">99 - 29</gadget>
<output>70</output>
70   Answer: 70
<result>E</result>
Before 7 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?