a)

4 · 22 = 4 · 20 + 4 · 2 = 80 + 8 = 88

3 · 28 = 3 · 20 + 3 · 8 = 60 + 24 = 84

7 · 51 = 7 · 50 + 7 · 1 = 350 + 7 = 357

5 · 16 = 5 · 10 + 5 · 6 = 50 + 30 = 80

b) 

6 · 60 = 6 · 6 · 10 = 360

3 · 120 = 3 · 12 · 10 = 36 · 10 = 360

2 · 240 = 2 · 24 · 10 =