Can someone help me understand proofs?

If f(x)=3x+1 and f^-1=x-1/3, then f^-1(7)=

Abakery recorded the number of muffins and bagels it sold for a seven day period. for the data presented, what does the value of 51 summarize? a) mean of bagels b) mean of muffins c) range of bagels d) range of muffins sample # 1 2 3 4 5 6 7 muffins 61 20 32 58 62 61 56 bagels 34 45 43 42 46 72 75

The ratios of boys to girls on a soccer league is 2: 5. if there are 28 boys, how many girls are playing soccer? extra points! will mark as brainiest asap