The answer of the above equation is 58.

Explaination:

Let the apartments be, A

the key be, K

& Let the painter be, P

So, formulating all the above equations in the above terms.

Equation (1); (A+K) + (A+K) + (A+K) = 39

Equation (2); K + K + K = 09

Equation (3); P + P + P = 15

Equation (4); A * P + (P+K) = ??

Now, initiating with equation (2);

K + K + K = 09

3K = 09

K = 03

Substitute the value of K in equation (1);

(A+K) + (A+K) + (A+K) = 39

(A+3) + (A+3) + (A+3) = 39

3A + 9 = 39

3A = 30

A = 10

Similarly, solve equation(3);

P + P + P = 15

3P = 15

P = 05

Now, substitute the values in final equation(4);

A * P + (P+K) = ??

= 10 * 5 + (5 + 3)

= 50 + 8

A * P + (P+K) = 58