to pay rent
rent charged under a lease agreement must be paid by the lessee even
if there is no express covenant in the lease document to that effect.
The rent being consideration must be certain or can be calculated
with certainty. For example, it may be expressed as $140/m2
of net lettable area which is certain as the total amount can be
calculated. A covenant can vary the rent according to some other
method such as being tied to an index.