Answer:
Joni's mistake was to multiply the exponents instead of adding the exponents.
Explanation:
we know that
When multiplying two powers that have the same base, you can add the exponents
so
![d^(3) *d^(11) =d^(3+11)=d^(14)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/oi67g7sv7e97ra7tik9sjphl9bruymb4nw.png)
Joni's mistake was to multiply the exponents instead of adding the exponents.