47. $8750 was invested at 12%, and $6250 was invested at 4%.

49. 10.5 ft by 6 ft

51. 15 and 8

53. The original width is 40 m, and the original length is 160 m.

55.

1. $C(x)=60\text{,}000+12x,R(x)=20x$

2. 

3. (7500, 150,000)

4. 11,129 timers

57. $450 for the single and $600 for the double

59. 3

61. Janet is 34, and Steve is 51.

63. They stole $35,000, and $15,000 went to Butch, $12,000 went to Sundance, and $8000 went to Billy.

65. $x=6,y=2$

67. She should build 4 two-story houses and 14 one-story houses to obtain a maximum profit of $96,000.

69. large: $60; medium: $52; small: $45