To write this as an algebraic expression, remember that twice a number means that 2 is being multiplied by a number. Since we are not solving, we can just use the variable n to represent the number that is being multiplied by 2. Finally, adding 5 to the number we will get the expression 2n + 5.
x is the "number" that is unknown, it's what's called a variable. Because you need two times a number(x) you put a coefficient of 2 in front of it, then simply add 5.
Examples with known variable values: 2(4)+5=13 2(2)+5=9
