ANSWER
C. 35 men
EXPLANATION
Let m represent the number of men needed and d represent the number of days.
From the question,the number of men needed varies inversely to the time needed to complete the project.
We can write the inverse variation equation.
where k is the constant of variation.
When m=28, d =90.
We substitute these values into the variation equation to determine the value of k.
Now the equation becomes:
When d=72,
Therefore he needs to have 35 men working.