Blood sugar results

I am wanting to construct a spread sheet for recording of blood test results and insulin dosage

In cell B3 I have a blood test value

In Cell I3 (correction dose) I am wanting a formula that if the number in cell B3 is equal to or less than 7 will inert a blank space in cell I3 I think this is =IF(B3=<7,” “)

however if the value in cell B3 is greater than 7 I want it to perform the function B3-7 I then want the product of that calculation to show in cell I3

For example:
Value of 6 in cell B3 types a blank space in cell I3
Value of 13 in cell B3 types 6 in cell I3

I don’t know how to do it and have found books either no help or incomprehensible! I believe it is called a nested IF function

This should do:

=IF(B3<=7,"",B3-7)

Thanks rollis13 it worked fine
Best regards
Matt

Glad being of some help .