Question 100964
a=12
c=2b+3
a^2+b^2=c^2
12^2+b^2=(2b+3)^2
144+b^2=4b^2+12b+9 expand.
3b^2+12b-135=0 subtract b+144 from both sides.
3(b-5)(b+9)=0 Factor.
b=5, b=-9 
b=5 is the only possible answer because the leg must be positive.
c=2b+3=2*5+3= 13 meters Ans.
Check:
144+25=169
Ed