28.90+49.99+d+d=100.39

Solution for 28.90+49.99+d+d=100.39 equation:

Simplifying
28.90 + 49.99 + d + d = 100.39

Combine like terms: 28.90 + 49.99 = 78.89
78.89 + d + d = 100.39

Combine like terms: d + d = 2d
78.89 + 2d = 100.39

Solving
78.89 + 2d = 100.39

Solving for variable 'd'.

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

Add '-78.89' to each side of the equation.
78.89 + -78.89 + 2d = 100.39 + -78.89

Combine like terms: 78.89 + -78.89 = 0.00
0.00 + 2d = 100.39 + -78.89
2d = 100.39 + -78.89

Combine like terms: 100.39 + -78.89 = 21.5
2d = 21.5

Divide each side by '2'.
d = 10.75

Simplifying
d = 10.75