For the sake of example, let's multiply the two numbers

and

together. Altogether, we have:

Rearranging the expression, we can group the exponents and coefficients together:

Multiplying each out, we notice that since

and

have the same base (10), multiplying them has the effect of adding their exponents, which leaves us with:

The takeaway here is that multiplying two numbers in scientific notation together has the effect of multiplying its coefficients and <em>adding</em> its exponents.
You just do 12•.65. Then that’s your answer.
You want to do to one side the same thing you do to the other side.
In order to get the n by itself you divide the 25n by 25. But in order to not change the answer you need to do the same to the 70.

so n=

which can be reduced to

so n=
Let m and h represent hours Mai spends mowing and hauling, respectively. Then (m+h) will be the number of hours Priya spends babysitting. In order for their earnings to be equal, we must have
7m +14h = 8.40(m+h)
Subtract 7m+8.40h: 5.60h = 1.40m
Divide by 1.40: m = 4h
Then the total number of hours worked by either person is
m + h = (4h) +h = 5h
When only whole numbers of hours are worked, the smallest number of hours that will make earnings equal is 5h, with h=1, or 5 hours. In that time, each will earn 5×$8.40 = $42.
Therefore, each of them must work 5 hours and earn $42 before they go to the movies and Mai will work 4 hours mowing and 1 hour hauling.