Order of Operations are PEMDAS. So, based on that, the answers would be:
1. 150. Do 20*5 first, as it's in parentheses, then multiply by 10.
2. 36. Same thing as #1 but different numbers.
3. 51. Do the stuff in parentheses first, then multiply because it gets priority over subtraction and then subtract.
4. 16. Do the multiplication in the parentheses first, then the subtraction, and then the division.