Question

A single tree produces about 2.6 × 10² lb of oxygen each year. The Amazon rainforest has about 3.9 X 10^11 trees.

Answer 1

$(2.6\times10^2) \times (3.9\times10^{11}) = 1.014\times10^{14}$

$1.014\times10^{14}$ <---How much is produced by all the trees in a year. 
They want how much each day so divide by 365


$\frac{1.014\times10^{14}}{365} = 2.77808\times10^{11}$
$2.77808\times10^{11}$ <---answer per day

Answer 2

10^11 is your answer hope it helps