JavaScript quiz question 1 part 7 my entry

This is my second entry to JavaScript quiz question no 1 seventh part.

Q 1 ----> part 7 )

a) x-- ;

here the output will be as follow
x is now 20
x is now 19
x is now 18
.
.
.
.
.
x is now 11

after this for loop will not execute as i will be greater than x.

b) x = x-20

output will be x is now 20.

c) x=x-i

here output will be as follow

x is now 20
x is now 20
x is now 19
x is now 17
x is now 14
x is now 10

d) x= x++ + --x

I don't know this part so please tell me the answer for this part.

thank you.