If you learn basic principles, all the problems look about the same.

We have i = 0.07

n = 40*26 = 1040

i12 = 0.07/12 = 0.00583333.....

i52 = (1+i12)^(6/13) - 1 = 0.0026880919907

r = 1+i52

P = $100

S = The Desired Accumulation.

That's all we need. Now build it. Note: Accumulations oftern are easier to build from the back.

Considering only the last payment, one week later, we have Pr

The second to last payment is Pr^2

See the pattern already?

Pr + Pr^2 + Pr^3 + ... + Pr^n = S

Pr(1 + r + r^2 + ... + r^(n-1)) = S

Pr((1 - r^n)/(1 - r)) = S

Ummm...We're about done. You do the rest.