What happens next?

How to improve your mathematical calculation skills
Start easy and take your time.
Don't jump straight in there trying to work out what' 235 x 958.7' equals, if you can do that you don't need to read this. Start with easier addition and subtraction questions, even if it is patronizing, make sure you can do them quickly.
Learn the multiplication tables and find the patterns in them. Knowing the patterns will make multiplication and division of larger numbers much simpler.