I have an equation to calculate `z` from multiplying several rasters and numbers as seen below:

    z <- a*b*c*d*e

The raster layers and values are as below:

    library(terra)
    set.seed(234)
    r <- rast(nrows=10, ncols=10)
    
    a <- setValues(r,runif(n = 100, min = 4, max=16))
    b <- setValues(r,runif(n = 100, min = 0, max=100))
    c <- setValues(r,runif(n = 100, min = 68, max=270))
    d <- 0.8
    e <- 7.9

I need to calculate uncertainty based on varying `c` and `e` by varying both variables as below:

`+/- 10` for `c`

`+/-` 4 for `e`

values need to change independently. In the end, I need to plot an uncertainty map.