21=4.2d

Solution for 21=4.2d equation:

Simplifying
21 = 4.2d

Solving
21 = 4.2d

Solving for variable 'd'.

Move all terms containing d to the left, all other terms to the right.

Add '-4.2d' to each side of the equation.
21 + -4.2d = 4.2d + -4.2d

Combine like terms: 4.2d + -4.2d = 0.0
21 + -4.2d = 0.0

Add '-21' to each side of the equation.
21 + -21 + -4.2d = 0.0 + -21

Combine like terms: 21 + -21 = 0
0 + -4.2d = 0.0 + -21
-4.2d = 0.0 + -21

Combine like terms: 0.0 + -21 = -21
-4.2d = -21

Divide each side by '-4.2'.
d = 5

Simplifying
d = 5