Alan

Use the square root button (√x) on the calculator.

Yes.  You can write this in the form y = 5 - 2x.  Different values for x will give different values for y.  When x changes, y also changes.

Click on the word "Scientific" on the right hand side of the input bar and choose "Fractions" from the menu that appears.

It depends on the context.  Sometimes it means the number e, which is approximately:

$${\mathtt{e}} = {\mathtt{2.718\: \!281\: \!828\: \!459\: \!045\: \!2}}$$

Sometimes it is used to represent 10 to some power, when used in, for example: 5e3, which would mean 5x10³

The latter use is common in some computing languages.

Let f be number of apartments in first building and s be number in second building.

Then we are told:

f + s = 15      ...(1)

2*f - 3*s = 5 ...(2)

From (1) we can write f = 15 - s

Replace f in (2) by 15 - s to get:

2*(15 - s) - 3s = 5

30 - 2s - 3s = 5

30 - 5s = 5

Subtract 5 from both sides 

25 - 5s = 0

Add 5s to both sides

25 = 5s

Divide both sides by 5

s = 5

Put this back into (1)

f + 5 = 15

Subtract 5 from both sides

f = 10

Percentage means parts out of 100. To find the percentage, first create the fraction (233/294) and then multiply by 100

(233/294)*100 ≈  79.25%

If the radius is 80cm the circumference is 2pi*80cm.

If the wheel rotates by 60° then a fraction 60/360 (= 1/6) of the circumference moves over the ground.  So the distance moved is 2pi*80/6cm

$${\frac{{\mathtt{2}}{\mathtt{\,\times\,}}{\mathtt{\pi}}{\mathtt{\,\times\,}}{\mathtt{80}}}{{\mathtt{6}}}} = {\mathtt{83.775\: \!804\: \!095\: \!727\: \!819\: \!7}}$$

or approximately 84cm

There is no ratio button as such.  Just enter the ratio as a fraction.