Could someone explain "variables on both sides of a complex equation"?

Step-by-step explanation:

Let's start with an equation like 2x+4=10. We have to isolate x to get an answer. We go for the number without the variable first.

2x+4=10

  Subtract 4 from both sides.

2x+4-4=10-4

2x=6

Divide by 2.

2/2=6/2

x=3

There you go!

1) c 2143.6 cm

2) c 113.0 m

3) a 33.5 ft

4)   d 2 cm

5) c 20 mm

6) 180 in

7) d 120 ft

the answer is 31.27mph