An isosceles triangle consists of two legs with equal length, and a base. So, we can call its three sides , where stands for base, and stands for leg.
Since the perimeter is the sum of the three sides, we have
In this case, the lengths of perimeter and base are known, so let's plug those values in the formula:
In order to solve for , let's subtract 0.4 from both sides...
...and divide both sides by 2:
So, the legnth of a leg is 0.3