How do you decide which details are important when determining how to find and compare unit rates

Galen sold tickets of his church’s carnival for a total of $2,820. children’s tickets cost $3 each and adult tickets cost $5 each. the number of children’s tickets sold was 30 more than 3 times the number of adult tickets slod. how many children’s ticket and how many adult tickets did he sell?

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The amount of data left on the cell phone six gb for 81.5 gb of data is used how much data is available at the beginning of the cycle