Function describing the solution of the differential equations describing the kinetic model with first-order terms for a two-way transfer from a free to a bound fraction, and a first-order degradation term for the free fraction. The initial condition is a defined amount in the free fraction and no substance in the bound fraction.

`SFORB.solution(t, parent_0, k_12, k_21, k_1output)`

- t
Time.

- parent_0
Starting value for the response variable at time zero.

- k_12
Kinetic constant describing transfer from free to bound.

- k_21
Kinetic constant describing transfer from bound to free.

- k_1output
Kinetic constant describing degradation of the free fraction.

The value of the response variable, which is the sum of free and
bound fractions at time `t`

.

FOCUS (2006) “Guidance Document on Estimating Persistence and Degradation Kinetics from Environmental Fate Studies on Pesticides in EU Registration” Report of the FOCUS Work Group on Degradation Kinetics, EC Document Reference Sanco/10058/2005 version 2.0, 434 pp, http://esdac.jrc.ec.europa.eu/projects/degradation-kinetics FOCUS (2014) “Generic guidance for Estimating Persistence and Degradation Kinetics from Environmental Fate Studies on Pesticides in EU Registration” Report of the FOCUS Work Group on Degradation Kinetics, Version 1.1, 18 December 2014 http://esdac.jrc.ec.europa.eu/projects/degradation-kinetics

Other parent solutions:
`DFOP.solution()`

,
`FOMC.solution()`

,
`HS.solution()`

,
`IORE.solution()`

,
`SFO.solution()`

,
`logistic.solution()`

```
plot(function(x) SFORB.solution(x, 100, 0.5, 2, 3), 0, 2)
```