SG chevron_right Primary 4 chevron_right Number and Algebra

I had spent like 45 minutes working through the various possibilities but still can't figure the answer out. So here is me waving my white flag. Maths expert pls help. My brain is exhausted from the 'strenuous' exercises I had just subjected it through. Thank you all in advance.

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Thank you Ms Yueh Mei for adding me to the group.

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Thank you for approved me and Hui Wen's thank again.

SG chevron_right Primary 3 chevron_right Measurement

I got the answer is 600cm but is wrong answer.Pls help.Thks.

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Thanks for accepting my request. I am horrible at Maths. I often take photos of my P3 girl's school Maths questions and post them in my Facebook wall for help. Now I can post here in this group for the Maths experts to help me out ☺