3.5-d+2.1=1.9

Solution for 3.5-d+2.1=1.9 equation:

Simplifying
3.5 + -1d + 2.1 = 1.9

Reorder the terms:
3.5 + 2.1 + -1d = 1.9

Combine like terms: 3.5 + 2.1 = 5.6
5.6 + -1d = 1.9

Solving
5.6 + -1d = 1.9

Solving for variable 'd'.

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

Add '-5.6' to each side of the equation.
5.6 + -5.6 + -1d = 1.9 + -5.6

Combine like terms: 5.6 + -5.6 = 0.0
0.0 + -1d = 1.9 + -5.6
-1d = 1.9 + -5.6

Combine like terms: 1.9 + -5.6 = -3.7
-1d = -3.7

Divide each side by '-1'.
d = 3.7

Simplifying
d = 3.7