Arithmetic answers:
1) 302
2) 207
3) 13
4) 4 or 1
12 3
5) 4089
6) 6555
7) 120
8) 4872
9) 1 6 or 1 1
12 2
10) 7.3
11) 0.66
12) 15
Starter answers:
Task 1) 
Task 2)
Task 3)
Challenge)
Mario is correct because he has successfully converting kilometres into metres. He remembered that to convert kilometres into metres, he needed to times by 1000.
Task 4)