A relatively large correlation coefficient, such as the 0.87 given here, indicates a direct proportion relationship between two variables. Here, as baby gains weight, smart phone pricing increases. Note that this is NOT a causal relationship.
The first is a. you can rewrite it

the second is d. the only common factor between 20 and 40 that can be taken out is the 4 which becomes a 2, but inside the square roots there is still a 5 and 10, which cannot be combined
the third is c.

the fourth is d.
add 3 to both sides

then square both sides

then divide both sides by 2, x=50
3 gallons of paint would cover 1050 square feet
(144) * (x^2)
(12^2) * (x^2)
(3^2) * (2^2^2) * (x^2)
3^2 * 2^4 * x^2