Oh the wrong answer got deleted so here I am :)
<span>Set up a system of equations. Let's make battery B and solar S where B and S represent the number of units.
</span><span>Step 1: The first two sentences talk about assembly.
</span>For Battery, it would be 10B.
For Solar, it would be 15S.
If you add 10B and 15S, it would take about 450 min total:
10B+15S=450
<span>Step 2: Now for the second equation. Both take 8 min, so 8B + 8S = 280 min.
Step 3: Solve for a variable. Let's do the second equation.
8B + 8S = 280 Subtracted 8B from both sides.
8S = 280 - 8B Divided both sides by 8 to get S by itself.
S= </span>
- B
<span>S = 35 - B Simplified, 280 divided by 8 = 35.
Now plug in S into the first equation.
10B + 15S = 450
</span><span>10B + 15(35-B) = 450
</span><span>10B + 525 - 15B = 450
</span>-5B = -75
B=15
Then you can plug in 15 for either of the first two equations to get S.
10B+15S=450
10(15)+15S=450
S=20
So 15 battery powered units and 20 solar powered units.