Due to the lack of information I assume these are fractions so for 5/35 we times it by 21 and 21 by 35 so they have the same denominator so now we got 105/735 and for 21 we get x/735 so now You put 105/735 and divide by 35 so we get back down to 21 for
3/21 for part 1
Now for part 2 again 15 times 20 and 20 times 15 to equal out the denominators so now we have 240/300 and x/300 so now plug 240 into x and divide down by 15 and now we get
16/20 for part 2
LMK if I am wrong I highly doubt it