The differential equation y+3y⁶=(y⁷+5x)y' can be written in differential form: M(x,y)dx+N(x,y)dy=0 where M(x,y)= , and N(x,y)=. The term M(x,y)dx+N(x,y)dy becomes an exact differential if _____
a) M(x,y) = 3y⁶ - y⁷ + 5xy
b) M(x,y) = 3y⁶ + y⁷ + 5xy
c) M(x,y) = 3y⁶ - y⁷ - 5xy
d) M(x,y) = -3y⁶ + y⁷ + 5xy