I am trying to make a speed calculator that takes speed input and distance needed to cover input and it should return the time needed to cover this distance based on the formula ‘speed = distance / time’, I also make the user input km if the distance is in kilometers or m if the distance is in meters and I use an If statement to turn the kilometers into meters.

io.write("enter speed(m/s):")
local speed = io.read()
io.write("enter distance needed:")
local distance = io.read()
io.write("specify((m) or(km)):")
local units = io.read()

local meters = "m"
local kilometers = "km"
local hundred

if units == meters then 
    local usedist = distance
elseif units == kilometers then 
    local usedist = distance * hundred
else
    io.write("you did not enter a valid character, please restart the program by pressing 'enter'")
    io.read()
end
print(usedist)
local timeneeded = usedist / speed
local timeneededh = timeneeded / 3600

os.execute("cls")

io.write("it will need "..timeneeded.." seconds or "..timeneededh.." hours")


io.write("n")
io.write("press the 'enter' key to continue")
io.read()

I was expecting a value of time in seconds but I got this

enter speed(m/s):5
enter distance needed:9
specify((m) or(km)):km
C:Lualua54.exe: object-time-calc.lua:15: attempt to mul a 'string' with a 'nil'
stack traceback:
        [C]: in metamethod 'mul'
        object-time-calc.lua:15: in main chunk
        [C]: in ?