You toss a coin and roll a number cube. find p(heads and an even number)

"and" means summe
P(coin)+P(cube)=1/2+1/6=0,666667
The chance to get head is always 1/2 no matter how often you toss the coin
And the chance to get a number when you roll a number cube is always 1/6

Did you mean that?

 there are 12 possible outcomes. 
Heads - 1 
Heads - 2 
Heads - 3 
Heads - 4 
Heads - 5 
Heads - 6 
Tails - 1 
Tails - 2 
Tails - 3 
Tails - 4 
Tails - 5 
Tails - 6 

You want heads AND an even number, so that narrows it down to three. 
Heads - 2 
Heads - 4 
Heads - 6 

So thats 3/12 chance, which is simply a 25.00 percent chance. 

Much simper way to do so is that are 4 outcomes if you don't count the numbers. 
Heads - Even 
Heads - Odd 
Tails - Even 
Tails - Odd 

so you can also get 25.0% that way.

A= r2 × 3.14 11×11 ↓ ↓ 121 × 3.14 = 379.94 → 379.9