Can someone pls help

Explain how you can use the associative property to evaluate (7x50)x4.

How do you find p(a and b) if a and b are independent events for two or more actions, such as tossing a coin twice and finding p(heads and heads)? 2. how do you find p(a or b) if a and b are independent events for one action, such as spinning a four-color spinner once and finding p(red or blue)?

X=-3y-5 3x+9y=7 how can u solve this?