1.

Swtich from fractional index to square root:

Square both sides:

Cross-multiply:

Expand (FOIL Method):

2.

Hehe, don't complicate yourself with logs. This is just a SAT question. Basically, what you do is try to get both bases to be the same. We can switch 8 to 2^3, so we get:

They're equal to each other, so the exponents has to be the same. Thus:

3. Percentage increase, very simple. What you do is subtract Elina's height at age of 6 from height at age of 12 and divide by height at age of 6.