## Elementary Technical Mathematics

$$13.6$$
Step 1: Substitute $x=-1$ and $y =5$. So, $(2.4-x)(x-xy)$ $(2.4-(-1))(-1-(-1*5))$ Step 2: Remember the order of operations: Parenthesis, Exponents, Multiplication/Division and Addition/Subtraction So first, Parenthesis $(2.4+1)(-1+1*5)$ Step 3: Next, Multiplication $(2.4+1)(-1+5)$ Step 4: Next, Addition and Subtraction $(3.4)(4)$ Step 5 Finish the multiplication. $13.6$