Utility question: check answer/help?

Question

if u(x1, x2)= 4(x1)^.5 +(x2) where x1 = units of nuts, x2 = units of berries

and Nathan originally consumed 16 units of nuts and 20 units of berries but now his consumption of berries is reduced to 12 units, how much nuts does he have to consume to keep him as happy as before?

would this be 36 nuts? i plugged in 16=x1 and 20=x2 and got 36 and used that # as the utility: then i plugged in that number as the utility and x2=12 to get x1 = 36

is this right?? if not, please tell me how to do it

Answer 1

4(16)^.5 + 20 = 36

then hold utility constant and add the new amt of berries:

4(x1)^.5 + 12 = 36

4(x1)^.5 = 24

(x1)^.5 = 6

x1 = 36

Yep, you did it correctly

Answer 2

Good job  that is the way to do it

See this econ stuff isn't so hard

Answer 3

Bingo. Yes you're right. This is assuming that the individual's level of utility unchange. :)