The easiest way to do this, in my opinion, is to multiply by 3 and then divide it by a nice even 100 (since it's 3 hundreths)
862.4 * 3 =
3 * 4 = 12
carry the 1
863.2
3 * 3 = 9
869.2
6 * 3 = 18
carry the 1
989.2
9 * 3 = 27
carry the 2
and you have 2769.2
then you just move it over two decimal spaces to get
27.692
So, 862.4 × 0.03 = 27.692