Evaluate. (Be sure to check by differentiating!) 1 ( 3 1 4 + 1 ) 1 3 at . . . Determine a change of variables from t to u. Choose the correct answer below. O A. u= 3t + 1 OB. u=+ + 1 O C. u=t O D. u= 3t* + 1 Write the integral in terms of u. [ ( 31 # + 1 ) 13 at = S Qu (Type an exact answer. Use parentheses to clearly denote the argument of each function.) Evaluate the integral. 1 ( 31 4 + 1 ) 1 3 at =