Write a reduced residue system modulo 24

5. A concert hall is constructed so that each row has 5 more seats than the row in front of it. If the first roW contains 15 seats, how many seats does the 30th row contain? (1) 155 (3) 165 (2) 160 (4) 170

28. In Example 9.7.5 it was shown that (a + b) = a* + 5a*b + 10a b² + 10a²b³ + 5ab* + b35. %3D Evaluate (a + b) by substituting the expression above into the equation (a + b) = (a + b)(a + b)³ and then multiplying out and combining like terms.

how would the u substitution work for the last two steps