Answer:
a. 8 years
b. $49.20
Explanation:
The computation is shown below:
a. The mark age is
Given that
232 is 8 times of the sum of mark and his sister ages
And, his sister is 21
So,
Let us assume the mark age be x
now
8(x + 21) = 232
x + 21 = 29
x = 29 -21
x = 8
b. The original price of the socks is
As each pair get $3 off
And she bought 6 pairs for $31.20
= $31.20 + 6 × $3
= $31.20 + 18
= $49.20