The way I like to solve proportions is by cross multiplying and dividing. First yo multiply the diagonals and then you divide by the other number. So if your proportion is 7/5 = x/3, your equation would be 7*3/5. So 7*3 is 21, so your equation is now 21/5. With some long division, you'll see that 21/5 = 4.2 That's your answer, feel free to ask more questions if you need!!(: