Answer is
Dimes = 47
Quarters = 31
Step by step
Dimes =.10
Quarters = .25
Dimes = q + 16
Quarters = q
Equation is .25q + .10d = $12.45
Substitute value of dimes in for d
.25q + .10( q + 16 ) = 12.45
Multiply
.25q + .10q + 1.6 = 12.45
Simplify
.35q + 1.6 = 12.45
Subtract 1.6 from both sides to isolate q
.35q + 1.6 - 1.6 = 12.45 - 1.6
Simplify
.35q = 10.85
Divide both sides by .35 to solve for q
.35/.35q = 10.85/.35
Simplify
q = 31
Quarters = 31
Now sub value of q into equation for dimes
Dimes = q + 16
Dimes = (31) + 16
Dimes = 47
Check your work
Dimes = .10 x 47 = $4.70
Quarters = .25 x 31 = $7.75
Total money = $12.45
Problem solved