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
The side length of the square concrete slab if the area is increased by 25% is 5feet
The formula for calculating the area of a square is expressed as:
A = L² where:
L is the side length of the square
Given the area of the square concrete slab = 20 square feet
20 = L²
L =√20
If the area is increased by 25%, new area will be:
An = 20 + (0.25*20)
An = 20 + 5
An = 25 sq.ft
Get the new length
An = Ln²
25 = Ln²
Ln = √25
Ln = 5feet
Hence the side length of the square concrete slab if the area is increased by 25% is 5feet
Learn more here: brainly.com/question/11300671
Avoiding conviniece store purchases
Here, regrouping is basically carrying.
64+43 shown vertically would be:
64
+43
-------
107
4+3 is 7, so seven is in the ones place, but that's not the point.
60+40 is 100, so you regroup by carrying the one to the hundreds place.
Hope I helped!