8. A man earns $3000 and his wife earns $1000 per month. They have two children. National insurance of 5% of all earnings must be paid before taxes are deducted. Allowances and tax rates are as follows: Table 5.11 Tax-free allowances Rates of taxable income $2000 per annum for 10% on first $2000 each adult 20% on next $2000 $500 per annum per child 30% on next $4000 - Earned income relief - 10% of husband's salary Non-taxable income - 50% of wife's salary 40% on the remainder Calculate: (a) the amount they paid for national insurance