I watched a edpuzzel and asked my teacher to explain it but i’m slow and still confused

Solve this system of equations. 12x − 18y = 27 4x − 6y = 10

Three times the sum of a number and seven is negative thirty-six. what is the number?

Find the directions in which the function increases and decreases most rapidly at upper p 0p0. then find the derivatives of the function in these directions. f(x,y)equals=x squared plus xy plus y squaredx2+xy+y2, upper p 0p0left parenthesis 1 comma negative 4 right parenthesis