Which of the following formulas is correct?

a$.$

Effective capacity $=$ Theoretical capacity $\backslash$times Safety capacity

b$.$

Capacity cushion $=$ Safety capacity $+$ Effective capacity

c$.$

Effective capacity $=$ Theoretical capacity $+$ Capacity Cushion

d$.$

Safety capacity $=$ Theoretical capacity $-$ Capacity cushion

e$.$

Capacity cushion $=$ Theoretical capacity $-$ Effective capacity