Emily drives from her house to her grandmother's house at a constant speed. On her way back, she increases her speed by 10 miles per hour, which allows her to save 1 hour on the return trip. If the one-way distance between Emily's house and her grandmother's house is 120 miles, find Emily's speed on her way to her grandmother's house. Let's think step by step and output the final answer within \boxed{}.
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