What is the constant of proportionality of the equation y = -1/4x

What number should be added to the expression x^2+3x+ in order to create a perfect square trinomial? 3/2 3 9/4 9

Extra points! find the missing dimension! need asap

Abaseball team drinks 10/4 gallons of water during a game. which mixed number represents the gallons of water consumed? a) 1 1/2 gallons b) 2 1/2 gallons c) 2 3/4 gallons d) 3 1/2 gallons