if a 2 - b 2 = 9 and a * b = 4, find a 4 + b 4.  Select the correct option.
A) 32
B) 90
C) 113
D) 92
E) 81
<gadget id="calculator">9 ** 2</gadget>
<output>81</output>

<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

<gadget id="calculator">16 * 2</gadget>
<output>32</output>

<gadget id="calculator">81 + 32</gadget>
<output>113</output>

<result>C</result>
if a 2 - b 2 = 9 and a * b = 4, find a 4 + b 4.
add(power(9, 2), multiply(power(4, 2), 2))
"a 2 - b 2 = 9 : given a 4 + b 4 - 2 a 2 b 2 = 92 : square both sides and expand . a * b = 4 : given a 2 b 2 = 42 : square both sides . a 4 + b 4 - 2 ( 16 ) = 81 : substitute a 4 + b 4 = 113 correct answer c"