2 hours and 40 minutes
Explanation:
Let a be Mrs Santos
Let b be Mr. Salonga
Mrs. Santos can cook the menu for a party in 4 hours
a = 4 hours
Mr. Salonga can work twice as fast as she can.
b = 2 ( 4) = 8 hours
The word time formula is
1/a +1 /b = 1/t
Where t is the total time
Substitute the values
1/4 + 1/8 = 1/t
1/4 + 1/8 = 2/8 + 1/8 = 3/8
Therefore
3/8 = 1/t
Doing cross multiplication
3*t = 1 * 8
3t = 8
Dividing both sides by 3
3t/3 = 8/3
t = 8/3 hours
t =2 \frac{2}{3}t=2
3
2
hours or 2 hours and 40 minutes