The equations are

                            Equation (1)

                          Equation (2)

Since the coefficients of the s-terms are same, you can eliminate these terms by adding the equations. Subtract the equations to eliminate variable s.

Write the equations in column form and subtract the corresponding columns.

Apply division property of equality: If a = b then

                                     (Divide each side by 10)

                                                (Cancel commmen terms)                                            

Now substitute –1 for t in either equation to find the value of s.

                                          (Equation 1)

                                   (Replace t = –1)

                                            (Multiply: )

Apply addition proparty of equality: If a = b then

                                (Add 5 to each side)

                                           (Additive inverse property: ) \ \

                                                 (Add: )

                                            (Divide each side by 6)

                                                   (Cancel commmen terms)

The solution is        

The solution is .