Answer: 90
Work Shown
LCM of x and y = ( x*y )/(GCF of x and y)
LCM of 9 and 10 = (9*10)/(GCF of 9 and 10)
LCM of 9 and 10 = (9*10)/1
LCM of 9 and 10 = 90
Side note: This formula works for 2 values only. If there are more than 2 values, then you'll need to recursively apply the formula to successive pairs of values.