We will solve this by using the order of operations.
P: Parenthesis
E: Exponents
M or D: multiplication or division (whichever comes first left to right.)
A or S: addition or subtraction
(Whichever comes first left to right.)
There are no parenthesis.
There are no exponents.
There is multiplication and division.
We will solve the division first because it comes first left to right.
20/2= 10
We will now solve the multiplication.
10 x 4= 40
We are left with 15-40+20.
We will now solve the addition and subtraction.
Subtraction comes first so we will solve this.
15-40=-25
We are left with -25+20.
-25+20=-5
-5 is your final answer.