Concept:Rewrite both sides of the equation using the same base, then compare the exponents.Explanation:Start with 16x=0.25.Convert 0.25 to a fraction:0.25=10025=41Since 41=4−1, the equation becomes:16x=4−1Rewrite 16 as 42:(42)x=4−1This simplifies to:42x=4−1The bases are equal, so equate the exponents:2x=−1Divide both sides by 2:x=−21Answer:x=−21, which is option A.