use the formula x3+y3 =(x+y)(x2-xy+y2)
then group 173 and 183 and 163 and 193 in both the cases x+y gives 35 take 35 as common from the entire expression the resultant expression within the bracket will be (16² - 16·19 + 19² + 17² - 17·18 + 18²)
the entire expression evaluates to be as even and hence the original expression is divisible by both 35 and 2 and hence by 70. So the resultant remainder is 0