How do you solve each expression by writing the solution in unit form and in standard form expression(2ten's1one) unit form and standard form

First let’s define Unit form and Standard form.
Unit form is where we are going to define or find the place value of the given numbers.
while standard form is where we are going to create an expanded form of the given numbers.

Given Number = 2 tens 1 one
Unit form
 2 is in the tens value and 1 is placed in ones value.
Thus, the number is 21.

Standard form.
Since 2 is placed in tens value 2 is equals to 20
and since 1 is place in ones value 1 is equals to 1
Therefore, the expanded form of 2 tens and 1 ones is :
=> 20 + 1
=> 21

B. because the 7 represents "seven times", x represents "a number", 12 represents "plus twelve", and -4 represents "minus four"