Question 748287
Use the Pythagorean Theorem:

{{{a^2+b^2=c^2}}}

{{{a^2+30^2=45^2}}}

{{{a^2+900=2025}}}

Subtract 900 from both sides:

{{{a^2=1125}}}

Take the square root of both sides:

{{{a= sqrt(1125)}}}

This may need to be reduced with radicals or approximated to a decimal, whichever the problem requires.