Help this girl out. This maths is killing me

Answer soon(fast) 15 pts-brainliest? for right answer with small explination a restaurant catered a party for 40 people. a child’s dinner (c) cost $11 and an adult’s dinner (a) cost $20. the total cost of the dinner was $728. how many children and adults were at the party? use the table to guess and check.(i couldn't get the graph onto the question)                                8 children and 32 adults9 children and 31 adults10 children and 30 adults12 children and 28 adults

Given: m zade = 60° and m2cdf = (3x + 15) prove: x = 15

Determine which solution is correct for solving 5/7y=6 reciprocals.