Question 1016450
Call the numbers of dimes and quarters, d and q.  Then we have
d + q = 200 and the value equation becomes
10d + 25q = 4250  (we work in cents)  
Now multiply the first equation by ten and subtract...
10d + 25q = 4250 
-(10d + 10q = 2000)
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15q = 2250
q = 150 quarters
d = 50 dimes