If the proportion of iris to roses in Nikki's garden is 2: 5, it means that for 25 roses: (2/5) = (10/25). Therefore to maintain the proportion by adding 20 roses: (2/5) = (18/45). The number of irises after the addition of roses will be 10 + 18 = 28 irises.
Put the number in the formula and do the arithmetic.
C = (5/9)(329 - 32)
C = (5/9)(297)
C = 165
The temperature in °C is 165.
Assuming you meant 45x^2y^2+18*3 , it should be 9(5x^2y^2+6)
