Step 1: Recall the law of sines formula

            FORMULA: \frac{a}{\sin A} = \frac{b}{ \sin B} = \frac{c}{\sin C}

                            Here each lowercase letter (like a) is the length of the side

                              opposite the vertex labeled with the same capital letter (like A).

Step 2: Find the unknown length by using the law of sines formula  

            From the figure

                      Since you know the measure of \angle T =25\degree , the length t of its opposite side,

                      And the measure of \angle S  = 22\degree

                      Use the Law of Sines to find the length s of the side opposite \angle S .

                            Law of sines

                                    \frac{s}{\sin S} = \frac{t}{\sin T}

                                   \frac{s}{\sin 22\degree} = \frac{15}{\sin 25}

                                     \frac{s}{0.374} = \frac{15}{0.422}  

                                   s = 0.374 *35.493

                                   s = 13,295