How to leftAnchor multiplier? - swift3

Question

I would like to use the for statement to give it left multiplier as many times as 'i'.
How do I write code?
I would definitely like to solve this problem.
Please help me
This is my code
for i in 0 ..< exchangeCategories.count {
let menuBtn: customButton = {
let menu = customButton(type: .system)
menu.item = i
menu.addTarget(self, action: #selector(scrollToPage(_:)), for: .touchUpInside)
menu.translatesAutoresizingMaskIntoConstraints = false
let name = exchangeCategories[i]
let label = UILabel()
label.text = name
label.font = UIFont(name: "SpoqaHanSans-Regular", size: 15)
label.textAlignment = .center
label.textColor = black_textColor
label.backgroundColor = white_backgroundColor
label.translatesAutoresizingMaskIntoConstraints = false
menu.addSubview(label)
label.topAnchor.constraint(equalTo: menu.topAnchor).isActive = true
label.leftAnchor.constraint(equalTo: menu.leftAnchor).isActive = true
label.rightAnchor.constraint(equalTo: menu.rightAnchor).isActive = true
label.bottomAnchor.constraint(equalTo: menu.bottomAnchor, constant: -2).isActive = true
let underLine = UIView()
if i == 0 {
underLine.backgroundColor = selectedPinkColor
label.font = UIFont(name: "SpoqaHanSans-Bold", size: 15)
label.textColor = pink_textColor
}
underLine.tag = i + 1 + 100
underLine.translatesAutoresizingMaskIntoConstraints = false
menu.addSubview(underLine)
underLine.leftAnchor.constraint(equalTo: menu.leftAnchor).isActive = true
underLine.rightAnchor.constraint(equalTo: menu.rightAnchor).isActive = true
underLine.heightAnchor.constraint(equalToConstant: 2).isActive = true
underLine.bottomAnchor.constraint(equalTo: menu.bottomAnchor, constant: 0).isActive = true
return menu
}()
wrap.addSubview(menuBtn)
menuBtn.topAnchor.constraint(equalTo: wrap.topAnchor).isActive = true
menuBtn.leftAnchor.constraint(equalToSystemSpacingAfter: <#T##NSLayoutXAxisAnchor#>, multiplier: <#T##CGFloat#>)
menuBtn.widthAnchor.constraint(equalTo: wrap.widthAnchor, multiplier: 0.25).isActive = true
menuBtn.bottomAnchor.constraint(equalTo: gap.topAnchor).isActive = true
}