I need to get that by using the for each function

1. Here's the approach I would take (to help you work it out for yourself):Treat each array as a single item in a new array (that is, your new array is a "list of lists")
2. iterate over that new array using a!forEach()
3. for each item in the array use the function that tells you how many items are in an array

Appian will take this as a single list of integers. To achieve what you want, the best solution I can think of is making a map for all individual arrays and then iterating over it using the keys.

a!localVariables(
  local!arrays: a!map(
    1: {1,2,3,8,9,9,9,9,9,80,90,70}, 
    2: {56,76,54,32}, 
    3: {20,23,45,54,32,54}, 
    4: {1,2,3,4,5,6,7}, 
    5: {11,12,13,14,15,16,17,18}
  ),
  a!forEach(
    items: a!keys(local!arrays),
    expression: "Length of array " & fv!index & " is " & length(local!arrays[fv!item])
  )
)

One more solution I found to this problem is using merge() function. The code is attached below.

a!localVariables(
  local!arr: merge(
    { 1, 2, 3, 8, 9, 9, 9, 9, 9, 80, 90, 70 },
    { 56, 76, 54, 32 },
    { 20, 23, 45, 54, 32, 54 },
    { 1, 2, 3, 4, 5, 6, 7 },
    { 11, 12, 13, 14, 15, 16, 17, 18 }
  ),
  local!size: {
    a!forEach(
      items: local!arr[1],
      expression: a!localVariables(
        local!temp: fv!index,
        a!forEach(
          items: enumerate(length(local!arr)) + 1,
          expression: if(
            a!isNullOrEmpty(local!arr[fv!item][local!temp]),
            0,
            1
          )
        )
      )
    )
  },
  a!forEach(
    items: local!size,
    expression: "length of array " & fv!index & " is " & sum(fv!item)
  )
)