Question 250796
Let's take it part by part.
Jimmy has seven times as many dimes as nickels. 
(i) d = 7n

Their value is $3.75.
(ii) 5n + 10d = 375

Putting these together, we get
(i) d = 7n
(ii) 5n + 10d = 375
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rewrite (i) as 
(iii) -7n + d = 0
(ii) 5n + 10d = 375
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multiply (iii) by -10 and eliminate d.
(v) 75n = 375 - - > n = 5. Now d = 35.