二元运算符'<'不能应用于'Double？'类型的操作数和'双'

I'm new to Swift and have searched some through the answers I've seen on this, but am trying to find out how to correct this problem. I have a Swift playground with code that runs fine and does not return this error, but have similar code in an iOS project that does return this error. It occurs when I'm comparing a fibers counted value to 5.5. I'm new to Swift and have searched some through