We are trying to find the unknown leg of the triangle and we can use the formula a^2 + b^2 = c^2.
5.3^2 + b^2 = 6.6^2
28.09 + b^2 = 43.56
28.09 - 28.09 + b^2 = 43.56 - 28.09
b^2 = 15.47
√b^2 = √15.47
b = 3,9331...
Lets round to the bearest hundreth.
3.9331... ≈ 3.93
Therefore, the length of the unknown leg is approximately 3.93cm.
Best of Luck!