Can anyone help me understand these output questions? (C++)

Question

i'm good at inputs, but very bad at outputs. I've taken these questions from the challenge game because even though it shows the right answer, it doesn't explain.

1. p = 8
cout << p++;
cout << ++p;

ANSWER : 810?

2. int x = 10;
void calculate (int&a) {
a = a + 10;
cout << a;
}
int main () {
int x = 20;
calculate (x);
cout << x+20;

ANSWER : 3050

3. int a = 2; int b = 1 ;
cout << (++a / b ++) * 5;

ANSWER : 15

Answer 1

1. ++x and x++ have a small difference.
++x:
First increments x by 1, then returns the value of x.
x++:
First returns the value of x, then increments x by 1.

3:
a = 2, b = 1
(++a / b++) * 5 can be thought as ((a+1) / b) * 5, a += 1, b += 1
So:
((2+1) / 1) * 5 = 3 * 5 = 15

Answer 2

Many people get confused with prefix and postfix increment (1 and 3 questions). Please refer to these existing questions

https://www.sololearn.com/discuss/1492044/?ref=app
https://www.sololearn.com/discuss/948304/?ref=app
https://www.sololearn.com/discuss/1562989/?ref=app

Answer 3

https://code.sololearn.com/c5dx79XNNrpD/?ref=app
Check this example also when you understand prefix and postfix