Cp(msol) = (msol)(msubst)(100%)

No.

Cp = msubst/msol x 100%

If you multiply BOTH sides by msol you get

msol x Cp = msol x msubst/msol x 100%

Can you cancel something?

Sir, algebra is not my strong point.

Don't sir me. And I already know you struggle.

Is there any other method or formula I could use?

Any other approach needs separate approach to each question, which doesn't make sense. Once you know how to rearrange formula and solve for particular unknown you have a tool to solve each question. Well, almost each question.

The only thing I know about the rate is the oxygen production: 93.0 mL / 60 s

The reaction that gives the oxygen is:

2 H2O2 --> 2 H2O + O2

So, I need to calculate the amount of moles of oxygen produced. Then I know the amount of moles of peroxide that are reacting away... which is the answer I need.

n = 93 g / 32g per mol

= 2.90635 mol

= 2.90635 mol / 60 seconds

= 0.0484375 mol / sec of O2 are created in reaction 2

Since there is twice the amount of H2O2, multiply 0.0484375 mol / sec by 2 to get

0.096875 mol/L s of H2o2

Therefore the rate is 0.096875 mol/L s ?

Could be you are on the right track, but you have started with 93 mL of gaseous oxygen and then it miraculously became 93 g of oxygen.