Answer:
you basically do the same things just backwards
Step-by-step explanation:
for example 9+9=18 well to double check your work all you do is flip to equation 18-9=9
Each coin will either land as a head or a tail. - 2 possible results.
for 5 coins its 2*2*2*2*2 = 32 different results.
B) 29
Because 20^2+21^2=c^2