Mari has 28 wooden cubes she what's to stack them to form a triangle each row will have one block fewer then the row below it how many blocks will be in the bottom row of the pyramid?

This is a problem involving the sum of numbers
one way is to just add them
1 row=1
2 row=3
3 row=6
4 row=10
5 row=15
6 row=21
7 row=28

each row has the number of blocks that is the row
7th row=7 blocks

so 7 blocks

The first thing we must do for this case is find the volume of the sphere.
 The volume is given by:
 V = (4/3) * (pi) * (r ^ 3)
 Where,
 A: Radius of the sphere
 Substituting values:
 V = (4/3) * (3.14) * (4 ^ 3)
 V = 267.95 in ^ 3
 Then, the weight of the sphere is:
 W = (267.95) * (0.75)
 W = 200.9625 pounds
 Round to the nearest pound:
 W = 201 pounds
 
 The weight of the sphere is:
 W = 201 pounds