There are twice as many Robins has blue jays and their 21 altogether how many blue jays are there

R + b = 21

2b = r

now we sub eq 2 into eq 1

r + b = 21

2b + b = 21

3b = 21

b = 21/3

b = 7

2b = r

2 (7) = r

14 = r

so there are 7 bluejays (b) and 14 robins (r) ... for a total of 21