East common multiple is the smallest multiple both numbers can go into. (Example: the LCM of 10 and 4 is 20, because both 10 and 4 go into 20 and 20 is the smallest number both 10 and 4 can go into. You could just multiply them both, but you'd get 40 and since its a bigger number it would be harder to work with.)
Least common denominator is just the least common multiple as a denominator. (Example: if you wanted to find the LCD of 5/7 and 1/10, you'd have to find the LCM of the demoniators (7 and 10) and then just use that as the denominator when adding fractions with unlikely denominators.) Sorry for such a long answer :P
The slope of the parallel line is -6/7 the slope of the perpendicular line is 7/6 the slope of the line = -6/7 the gradient of two parallel lines are equal the product of the gradient of two perpendicular lines is -1 : the gradient m1*m2 = -1 m2= -1(-6/7) m2= 7/6
