2 + 22 = 15, 4 + 16 = 16, 6 + 10 = 17 and 8 + 4 = 18 There must be certain common multiples, x and y, that make the real value of left-hand side(LHS) in each expression above equal to the real value of its right-hand side(RHS): x for the 1st terms of each LHS, { 2, 4, 6, 8 }, and y for the 2nd terms of each LHS, { 22, 16, 10, 4 }.
So that, the expressions above can be rewritten in their real values, assuming the number of each RHS shows the real value of its LHS: 2x + 22y = 15 ··· Eq.1, 4x + 16y = 16 ··· Eq.2, 6x + 10y = 17 ··· Eq.3, 8x + 4y = 18 ··· Eq.4. From Eq.1 and Eq.2, we have: x = 2 and y = 0.5.
CK: Plug these values of x and y into each LHS of Eq.1, Eq.2, Eq.3 and Eq.4. 2·(2) + 22·(0.5) = 15, 4·(2) + 16·(0.5) = 16, 6·(2)+10·(0.5) = 17 and 8·(2) + 4·(0.5) = 18 CKD.
Thus, in each given expression, the 1st term of LHS indicates 2 times of its number, the 2nd term of LHS indicates one half of its number, and the number of RHS expresses the real value of LHS.
Therefore, the answer is 10 + 10 = 25 {=10·(2)+10·(0.5)}