Answer:
The value is 
Step-by-step explanation:
Generally the productivity rate is mathematically represented as

Here K is the ha the farmer could harvest in an hour and Z is a typical yield of corn in kg/ha
Now considering 1970
The productivity rate is

=>
Now considering 1940
The productivity rate is given as
Generally the productivity ratio is mathematically ration is mathematically represented as

=> 
=> 
The sum of the equation is
and it can be determined by using addition and it can be determined by summation rule in the equation.
<h2>Given that,</h2>
Equation; 
<h3>We have to
determine</h3>
The sum of the equation.
<h3>
According to the
question,</h3>
To determine the sum of the equation following all the steps given below.
<h3>
Equation;

</h3>
The sum of the equation is determined by factorizing the equation,
Then,
The sum of the equation is,

Hence, The required sum of the equation is
.
For more details about Addition refer to the link given below.
brainly.com/question/25996972
Answer:
the first one -4 and -4
Step-by-step explanation:
-4 times -4 is 16 because the negatives cancel out