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Determine the value of k such that the points A(2,3), B(4,k), and C(6,-3) lie on the same straight line.

Solve the given equation for ?. Find the approximate value.

(3/5 of 399.78 + 7/9 of 360.15) ÷ (√63.94 + 25% of 383.94) = ?

[{(√785) % of 449.85}/(35.89 × 7.14 + 849.89 ÷ 5.12 + 199.78% of 41.09)] = ( 1/? ) 

65.22 of 359.98% + 459.99 ÷ 23.18 = ?

{(23.65 × 35.12) ÷ 6.97} + 179.86 = ? × 14.76

What will come in place of the question mark (?) in the following series?

50, 25, 25, ?, 75, 187.5

What approximate value will replace the question mark (?) in the following?