let x be the current age.
since x is a multiple of 7 and is greater than 20 but less than 80
by trial and error:
7x3=21+1 = 22 but not a multiple of 5
7x4=28 +1 = 29 but not a multiple of 5
7x5=35+1 = 36 but not a multiple of 5
7x6=42+1 = 43 but not a multiple of 5
7x7=49+1 = 50 is a multiple of 5
7x8=56+1 =57 but not a multiple of 5
7x9=63+1 = 64 but not a multiple of 5
7x10=70+1 = 71 but not a multiple of 5
7x11=77+1 = 78 but not a multiple of 5
7x12=84+1 = 85 is a multiple of 5 but more than 80
so x = 49
age 6 years from now
x + 6 = 49 + 6 = 55
answer is 55
