#6 is using using ratios:
7/2x+4 = 4/x+3 =
8x+16 =7x+21 =
8x=7x+5 =
x=5
AC = 2(5)+4= 14 + 5+3=8, 14+8 =22
#7
ratio of known sides 9/4 =2.25 now multiply other 2 sides by 2.25
7*2.25 = 15.75
9*2.25=20.25
perimeter = 9 +15.75+20.25 = 45
