In every 45-45-90 triangle, both legs have the same length and the hypotenuse has the length of a leg multiplied by √2.
The hypotenuse is the side opposite to the right angle (90º). The other two sides are the legs that have the same length.
In the question b., the hypotenuse has a length b and the missing leg has a length a.
Since the leg of the triangle has a measure of 2.5ft, then the leg a must have the same measure. Then:

The hypotenuse has the length of a leg multiplied by √2. Then:
![\begin{gathered} b=2.5*\sqrt[]{2}ft \\ =\frac{2*2.5*\sqrt[]{2}}{2}ft \\ =\frac{5\cdot\sqrt[]{2}}{2}ft \\ \approx3.5355\ldots ft \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/mvf0citqsjtxsjcghobl97rkbi19hwwlr8.png)
Therefore, the lengths of a and b in the question b., are:
![\begin{gathered} a=2.5ft \\ b=\frac{5\cdot\sqrt[]{2}}{2}ft\approx3.5ft \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/2h20yqry25137yc6aha05aqjzv2g84uc3b.png)