Explanation:
r = 250 ( thousand) and r = 180 + 35 log4 (x) <====base 4 LOG
 sooooo 250 = 180 + 35 log4(x) find 'x' thousands
 (250 -180)/35 = log4 (x) 
 2 = log4(x) these are exponents of 4 ...anti log base 4:
 4^2 = 4^(log4 x)
  16 = x  
 But x is thousands of $ (per the question info)
  so $ 16 000