Concept:Express each base-b numeral as a polynomial in b, then solve for b.Explanation:Let the unknown base be b.The given addition in base b is:465b+24b+225b=1050bRewrite each numeral using powers of b:(4b2+6b+5)+(2b+4)+(2b2+2b+5)=b3+5bCombine like terms on the left:6b2+10b+14=b3+5bRearrange to form the equation:b3−6b2−5b−14=0Test b=7:73−6(72)−5(7)−14=343−294−35−14=0Since b=7 satisfies the equation and all given digits are less than 7, base seven is valid.Answer:D. seven