After the statements that follow are executed,
var firstName = "Ray", lastName = "Harris";
var fullName = lastName;
fullName += ", ";
fullName += firstName;

a. firstName="Harris"
b. firstName="Ray Harris"
c. fullName="Ray Harris"
d. fullName="Harris, Ray"

d. fullName="Harris, Ray"

Explanation:

// here we define two variables firstName="Ray" and lastName= "Harris"

var firstName = "Ray", lastName = "Harris";

// then we create another variable fullName and assign it the value stored in variabl lastName that is "Harris"

var fullName = lastName;

// then we added a coma and space. At this point fullName= Harris,

fullName += ", ";

// then we added firstName to the variable fullName. At this point fullName=Harris, Roy

fullName += firstName;

Note: the += operator means that add the variable on the left by an amount on the right

a+= b; or a = a + b; both mean same

the answer to your question would be something called hertz. the unit of measurement called a hertz, which is one cycle per second, is used to measure clock speed. within one cycle, your computer processes, refreshes, or updates itself to the changes that it is going through. in the case of computer clock speed, one hertz equals one tick per second. the clock speed of computers is usually measured in megahertz (mhz) or gigahertz (ghz)