An angle of 1º can be divided into 60 equal parts.
Each of these parts is known as 1 minute (1').
So 60' = 1º
Convert 42.45º into an angle in degrees and minutes.
Just look at the part after the decimal point i.e. 0.45º
Use a calculator to work out 0.45 × 60 = 27
So 42.45º = 42º 27'