If m = -9 and n = 13, find the value of 25m² + 40mn +16n²

Correct option is B

​Given:

m = -9, n = 13.

Solution:

$$25m^2 + 40mn + 16n^2 = (5m + 4n)^2$$ 

Then, 

​$$5m + 4n = 5(-9) + 4(13) = -45 + 52 = 7$$ 

So, 

​$$(5m + 4n)^2 = 7^2 = 49.$$​​