Well because m∠GBH is equal to m∠HBC all you have to do is 28 add to 28. We know that m∠GBH is equal to m∠HBC because of the two dashes marked in the angles and because m∠GBC = m∠GBH + m∠HBC this can be rewritten as m∠GBC = 28 + 28 adn from there we can find out that m∠GBC = 56°.
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