We can use number operators on variables that hold number values:

$tadpole_age = 7;
$lily_age = 6; 
$age_difference = $tadpole_age - $lily_age;
echo $age_difference; // Prints 1

Let’s look at another example of performing operations with number variables:

$favorite_num = 22;
echo $favorite_num + 1; // Prints 23
echo $favorite_num; //Prints 22

In the code above, we created the variable $favorite_num then we used echo to print that value plus 1. Note that we didn’t reassign the value of the $favorite_num variable, so it still had the value 22 when we printed it on the last line.

We reassign number variables using the assignment operator:

$age = 82;
echo $age; // Prints: 82

$age = $age + 2;
echo $age; // Prints: 84

Let’s do some addition and subtraction with variables!