a=49−x2​−25−x2​ and b=49−x2​+25−x2​.
Then ab=(49−x2)−(25−x2)=24, so b=a24​=324​=8.
The given equation can be solved directly. Adding 25−x2​ to both sides of the equation and squaring leads to 15=625−x2​. Solving for x2 gives x2=475​. Substituting this value into 49−x2​+25−x2​ gives the value (A)8​.