1.16 : 8 = x : 5
16x
- = -
8 5
x × 8 = 16 × 5
x = 10

2.25 : 15 = 10 : x
2510
- = -
15 x
x × 25 = 15 × 10
x = 6

3. 236 : 2 = 4543 : x
x × 236 = 2 × 4543
x = 38.5 hours

4. 12 : 52 = 18 : x
x × 12 = 52 × 18
x = 78 pounds