You need to use pythagorus theorem!
a^2 + b^2 = c^2
Hypotenuse will ALWAYS be variable “c” ur two other sides can be either “a” or “b”
In this case we are finding either “a” or “b”
So c^2 - b^2 = a^2
Now substitute!
a^2 = 15^2 - 2^2
a^2 = 225 - 4
a^2 = 221
Now to finish we need to square root this! Since we are square rooting 221, “a” will loose the exponent “2” and become only “a”
a = 14.9
Ur done!!! Lmk if u need better explanation!