Hey you are on the right track, if you simply sketch out the given lines you will see that a right angled isosceles triangle. The two equal sides of the triangle will be "a"
Now as we know area of a triangle = 1/2*(b)*(h), here b=h=a,
hence 1/2*(a)(a) = 8 ( area is given as 8)
a^2 = 16
so a = 4
Also alternately, if you double the triangle you will get a Square of side "a"
whose area will be +> a*a=2*8
hope this helps you out
hope that helps you out