Math help pls all 4 questions please

Me. i can't figure out this question. give an explanation too. .

Which coefficient matrix represents a system of linear equations that has a unique solution ? options in photo*

Awater truck is filling a swimming pool. the equation that represents this relationship is y=19.75x where y is the number of gallons of water in the pool and x is the number of minutes the truck has been filling the pool.