It is B because you have to subtract and than you have to add
Step-by-step explanation:
For square
A=bh
A=30(20)
A=60in²
For triangle
A=½bh
A=½(40)(30)
A=½(120)
A=60in²
Add
60+60=120in²
Answer:
Joint variation says that:
if
and 
then the equation is in the form of:
, where, k is the constant of variation.
As per the statement:
If x varies jointly as y and z
then by definition we have;
......[1]
Solve for k;
when x = 8 , y=4 and z=9
then
Substitute these in [1] we have;

⇒
Divide both sides by 36 we have;

Simplify:

⇒
to find z when x = 16 and y = 6
Substitute these value we have;

⇒
Multiply both sides by 9 we have;

Divide both sides by 12 we have;
12 = z
or
z = 12
Therefore, the value of z is, 12
He should start cooking at 15:00