0=65-(2.1*d)

Solution for 0=65-(2.1*d) equation:

Simplifying
0 = 65 + -1(2.1d)

Remove parenthesis around (2.1d)
0 = 65 + -1 * 2.1d

Multiply -1 * 2.1
0 = 65 + -2.1d

Solving
0 = 65 + -2.1d

Solving for variable 'd'.

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

Add '2.1d' to each side of the equation.
0 + 2.1d = 65 + -2.1d + 2.1d
Remove the zero:
2.1d = 65 + -2.1d + 2.1d

Combine like terms: -2.1d + 2.1d = 0.0
2.1d = 65 + 0.0
2.1d = 65

Divide each side by '2.1'.
d = 30.95238095

Simplifying
d = 30.95238095