We know, two angles are said to be complementary, if the sum of their measures is 90∘.
Let the angle be x∘ and its complement is 90∘−x∘
Then, according to the statement,
⇒x∘−(90∘−x∘)=12∘
⇒x∘−90∘+x∘=12∘
⇒2x∘=12∘+90∘=102∘
⇒x∘=102∘2=51∘.
Hence, the measure of the angle is x=51∘
and its complement is 90o−x=90o−51o=39∘.