Ireally don't understand what they are asking but i understand 12 is c

Since it is an isosceles triangle, both legs are congruent. So you could use the 
a^2+b^2=c^2

but since two legs are equal it would be 
a^2+a^2=c^2
2a^2=144^2
2a^2=20,736
a^2=20736 / 2
a^2=10,368
square root of a^2=square root of 10,368
a=square root of 10,368 or 101.82