Answer
$2.15$ x $10^{20}$
Work Step by Step
Human brain: $3$ x $10^{10}$ neurons
Gorilla brain: $7.5$ x $10^{9}$ neurons
Combine the coefficients and exponents. Then add $1$ to the exponent since scientific notation will put the decimal point one more place to the left.
$3$ x $10^{10}$ x $7.5$ x $10^9$
$21.5$ x $10^{19}$
$2.15$ x $10^{20}$
