Verified Answer :

HeathyCigar

(a)=16 

First you do 428. Then 428=336. Divide 336 by 21 to find (a) which equals 16.

(r)=5

First you do 1058. Then 1058= 840. Divide 840 by 168 to find (r) which equals 5.

texaschic101

these are proportions and can be solved by cross multiplying and solving for the variable.

8/a = 21/42
cross multiply
(21)(a) = (8)(42)
21a = 336...divide both sides by 21
a = 336/21
a = 16
also, u will notice that : 8/16 is equivalent to 21/42...because proportions are nothing but equivalent fractions.

105/168 = r/8
cross multiply
(168)(r) = (105)(8)
168r = 840...divide both sides by 168
r = 840/168
r = 5

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