Answer:
B) Cube
Step-by-step explanation:
A) square pyramid has one square base and 4 congruent triangles
B) Cube has 6 congruent squares
C) Rectangular pyramid has one rectangle base and 4 congruent triangles
D) Rectangular prism has 3 sets of rectangles; total of 6 rectangles

Above step we use "Multiplication property of equality"

In the above step we "Simplify on both sides of equation"

In the above step we use "Distribution property"

The above step is the result of using "Subtraction property of equality"

Above step is result of "Combining the like terms"

Above step is the result of using "Division property of equality"

Above step is result of "Simplifying fractions on either side of equation"
30=(10*3*x)/2
*2 *2
60=10*3*x
60=30x
60/30=30x/30
2=x