Which number can replace the variable to make these fractions equivalent? blank/7, 54/42

Equivalent fractions can be found by multiplying numerator and denominator by the same number.

for example : 2/5 * 3/3 = 6/152/5 and 6/15 are equivalent. Just like 2/5 * 4/4 = 8/202/5 and 8/20 are equivalent...so basically, if u multiply the numerator by a certain number, and the denominator by that same number, u will get an equivalent fraction.

Now to ur problem...
   x             54
   =  
   7             42

now look at ur denominators7 x what = 42 ? 7 x 6 = 42...so u have multiplied the denominator by 6so u would have to multiply the numerator by 6or divide by 654/6 = 9or 9 x 6 = 54. So that missing value is 9.

9/7 = 54/42

check..
9/7 * 6/6 = 54/42 (equivalent)

the answer would be c ≈ 18.852*3.14= 6.286.28*3=18.85